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UNIVERSITY  OF  CALIFORNIA. 


\  Class       J 


WORKS   OF 
PROFESSOR   FORREST  JONES 

PUBLISHED    BY 

JOHN    WILEY  &  SONS 


The  Gas  Engine. 

ix  +  447  pages,  142  figures.     8 vo,  cloth,  $4.00. 

Machine  Design.      Part  I.   Kinematics  of 
Machinery. 

Fourth  Edition,  Revised.     vi  +  182  pages,  134 
figures.     8vo,  cloth,  $1.50. 

Machine  Design.  Part  II.  Form,  Strength, 
and  Proportions  of  Parts. 

Third  Edition,  Revised  and  Enlarged.     ix  + 
4  U  pages,  186  figures.     8vo,  cloth,  $3.00. 


THE  GAS  ENGINE 


BY 


FORREST    R.  JONES 


FIRST  EDITION 
FIRST    THOUSAND 


NEW   YORK 
JOHN    WILEY   &    SONS 

LONDON  :    CHAPMAN   &   HALL,  LIMITED 
1909 


COPYRIGHT,  1909, 

BY 
FORREST    R.  JONES 


Stanhope  Ipress 

F.  H.  CILSON    COMPANY 
BOSTON.     U.S.A. 


PREFACE. 


THE  following  discussion  of  gas  and  oil  engines  is  presented  in 
the  manner  which  it  is  believed  is  the  most  suitable  for  a  text- 
book for  class  instruction  and  for  directing  laboratory  experi- 
mentation, as  well  as  for  meeting  the  needs  of  those  who  wish  to 
learn  to  operate  commercially  and  to  test.  The  general  con- 
secutive order  is:  Descriptive,  operative,  testing  for  faults, 
theoretical,  results  of  trials.  The  latter  portion  deals  some- 
what briefly  with  thermodynamics  and  theoretical  cycles. 

Gas  producers  are  considered  briefly  from  both  the  practical 
and  theoretical  viewpoints,  the  aim  being  only  to  give  a  clear 
insight  of  the  principles  and  methods  of  manufacturing  gas  for 
power  purposes. 

The  methods  of  locating  and  eliminating  troubles  have  been 
given  in  considerable  detail.  The  writer's  experience  in  training 
something  more  than  a  hundred  men  in  the  commercial  operation 
of  gas  and  oil  engines  has  been  fully  convincing  as  to  the  need 
of  complete  instruction  in  this  particular. 

The  illustrations  are,  with  one  or  two  exceptions,  representative 
of  American  practice,  but  the  text  is  based  on  information  gained 
by  personal  observation  of  motors  in  Germany,  Belgium,  France, 
and  England,  as  well  as  operating  experience  in  America. 

The  proof  was  kindly  read  by  Mr.  Charles  E.  Ferris,  Professor 
of  Mechanical  Engineering,  and  the  electrical  portion  also  by 
Mr.  Charles  E.  Perkins,  Professor  of  Electrical  Engineering,  both 
in  the  University  of  Tennessee.  The  criticisms  and  suggestions 
of  these  gentlemen  led  to  important  modifications  and  additions. 

F.  R.  J. 

DECEMBER  21,  1908. 


iii 

195087 


CONTENTS. 


CHAPTER   I. 

PAGE 

TYPES  OF  MOTORS,  IMPULSE  FREQUENCY,  SCAVENGING,  REVERSING.         i 

i.  Introductory.  2.  Beau  de  Rochas-  or  Otto-cycle  motor.  3.  Four- 
cycle motors.  4.  Auxiliary  exhaust  port.  5.  Atkinson  four-cycle 
motor.  6.  Complete  expansion  gas  engine.  7.  The  Nuremberg  and 
Gobron-Brillie  motors.  8.  Two-cycle  motors.  9.  Koerting  two-cycle 
motor.  10.  Brayton  motor  and  cycle,  n.  Oil-burning  motors. 
12.  Hornsby-Akroyd  oil  motor.  13.  Oil-burning  motor  with  bulb 
ignition.  14.  Diesel  oil  motor.  15.  Pioneer  types.  16.  Scavenging. 
17.  Compound  motors.  18.  Impulse  frequency  for  different  arrange- 
ment of  cylinders.  19.  Reversing  the  rotation  of  the  motor. 


CHAPTER   II. 

CARBURATION,  CARBURETERS,  PREHEATING  THE  CHARGE,  FUEL  SUPPLY      47 

20.  Carburation  of  air.  21.  Primer  for  carbureter  using  volatile 
fuel.  22.  Float-feed  carbureter.  23.  Pump-feed  spray  carbureters. 
24.  Pump-feed  carbureter  with  measuring  cup.  25.  Disk-feed  spray 
carbureter.  26.  Diaphragm-feed  spray  carbureter.  27.  Spray  car- 
bureters in  general.  28.  Other  types  of  carbureters  for  naphtha 
and  gasoline.  29.  Cooling  effects  of  vaporization.  30.  Heating  the 
carbureter  or  the  air.  31.  Carbureters  for  kerosene  and  other  non- 
volatile liquids.  32.  Early  and  obsolete  forms.  33.  Effect  of  pre- 
heating the  charge  on  the  power  of  the  motor.  34.  Fuel  supply  for 
carbureters. 

CHAPTER   III. 

IGNITION 63 

35.  General.  36.  Double  ignition.  37.  Low-tension  electric  arc  igni- 
tion. 38.  Sources  of  electric  supply  for  ignition.  39.  Low-tension 
arc  igniter  with  solenoid  circuit  breaker.  40.  Oscillating  electric  gen- 
erator for  low-tension  ignition.  41.  Induction  coil  for  low-tension 
intermittent  current.  42.  High-tension  jump-spark  electric  ignition 
in  general.  43.  Spark  plugs.  44.  Timers  for  high-tension  electric 
ignition.  45.  Induction  coils  for  electric  ignition.  46.  Electric  bat- 
teries. 47.  Dry  batteries.  48.  Series  and  multiple  batteries.  49.  Mul- 
tiple series  batteries.  50.  Arrangement  of  batteries  for  ignition. 
51.  Recuperation  of  dry  cells.  52.  Storage  batteries,  accumulators, 
secondary  batteries.  53.  Comparison  of  dry  cells  and  storage  bat- 
teries for  ignition  purposes.  54.  Testing  electric  batteries.  55.  Wir- 
ing scheme  for  single-acting,  single-cylinder  motor  with  jump-spark 
ignition.  56.  Wiring  scheme  for  motor  with  more  than  one  combus- 

v 


vi  CONTENTS 

IGNITION  —  Continued  PACK 

tion  chamber.  57.  Jump-spark  ignition  with  .high-tension  distrib- 
uter. 58.  Comparison  of  multi-induction  coil  and  high-tension  dis- 
tributer systems.  59.  Jump-spark  ignition  in  two  cylinders  with  one 
induction  coil  and  no  distributer.  60.  Magneto  generator  for  jump- 
spark  ignition.  61.  Low-tension  magneto  and  separate  transformer 
system.  62.  High-tension  magneto.  63.  Dynamo-battery  ignition 
system.  "Floating  the  battery  on  the  line."  64.  Hot-tube  ignition. 
65.  Hot-metal  igniter  heated  by  internal  combustion.  66.  Hot-wire 
and  platinum-sponge  igniters. 

CHAPTER   IV. 

CONTROL  OF  POWER  AND  SPEED 115 

67.  General  methods.  68.  Fuel  control.  General.  69.  Fuel  control 
in  four-cycle  gas  or  vapor  motor.  70.  Governing  and  hand  control. 
71.  Hit-or-miss  governing.  72.  Hit-or-miss  governing  by  omitted  open- 
ings of  the  mixture  inlet  valve.  Four-cycle  motor.  73.  Hit-or-miss 
governing  by  keeping  the  exhaust  valve  open  during  the  suction  stroke. 

74.  Keeping   the   exhaust   valve   closed   during   the   exhaust   stroke. 

75.  Keeping  the  fuel  valve  closed  and  opening  the  mixture  inlet  valve 
to  admit  air.     76.  Modern  modified  method  of  cutting  out  charges. 
77.  Governing  by  varying  the  amount  of  fuel  admitted  for  an  explo- 
sion.    78.  Throttling.     79.  Governing  by  the  mixture  inlet  valve  to 
reduce  the  charge.     80.  Governing  by  fuel  valve  to  reduce  the  charge. 
81.  Governors.       General.       82.  Hydraulic    governors.       83.   Hand 
control  of  speed  and  power.     General.     84.  Early  and  late  ignition. 
Definitions.     85.  Early  and  late  ignition  effects  on  power  and  speed. 
86.  Time  of  ignition  as  affected  by  degree  of  compression.     87.  Lag 
in  jump  spark  ignition  apparatus.     88.  Hand  control  by  throttle  and 
spark.     89.  Combined  hand  control  and  governing.     90.  Compara- 
tive accuracy  of  methods  of  governing.     Speed  variation  in  cut-out-of- 
charge    governing.     91.  Speed    variation    with    throttle    governing. 
92.  Uniformity  of  speed  in  two-cycle,  governed  motor. 

CHAPTER  V. 
COOLING  THE  MOTOR 162 

93.  General.  94.  Air  cooling.  95.  Water  cooling.  Thermal  circula- 
tion. Circulating  pump.  96.  Water-cooled  pistons  and  valves. 
97.  Oil  cooling.  98.  Gaskets  and  packing  materials.  99.  Pump 
packing. 

CHAPTER  VI. 

LUBRICATION  OF  MOTOR 171 

100.  Oils  and  methods  of  applying.     101.  Lubricators. 

CHAPTER  VII. 

DISPOSAL  OF  EXHAUST  GASES 177 

102.  Precautions.  103.  Silencing  the  exhaust.  104.  Subterranean 
mufflers  and  silencers.  105.  Exposed  muffler.  106.  Submerged  ex- 
haust pipe.  107.  Muffler  cut-out.  108.  Momentary  back  pressure. 


CONTENTS  vii 

CHAPTER  VIII. 
STARTING  AND  ADJUSTING  THE  MOTOR 181 

109.  Methods  of  starting,  no.  Relieving  compression,  in.  Prepara- 
tions. 112.  Starting  small  gas  motor  by  cranking.  113.  Starting 
small  gasoline  motor  by  cranking.  114.  Starting  a  large  gas 
motor  by  external  power.  115.  Starting  the  motor  by  its  own 
impulse.  116.  Starting  on  "compression."  117.  Starting  by  firing 
blank  cartridge  in  cylinder.  118.  Stresses  due  to  starting  motor 
by  its  own  impulse.  119.  Compressed  air  for  starting.  120.  Starting 
single-cylinder,  single-acting  motor  by  compressed  air.  121.  Start- 
ing motor  with  more  than  one  combustion  chamber  by  compressed  air. 
122.  Lubricator  adjustment.  123.  Cooling- water  adjustment.  124.  Ad- 
justing spray  carbureters  and  the  ignition.  125.  Rich  and  lean  fuel 
mixtures.  126.  Rough  adjustments  for  black  smoke  and  backfiring. 
127.  Adjustment  of  a  cut-out-governed  motor.  128.  Adjustment  of  a 
throttle-governed  motor.  129.  Adjustment  of  a  variable-speed  motor 
with  hand  control.  130.  Adjustment  of  carbureter  on  an  automobile. 

131.  Adjustment  of    carbureter    and    ignition   on  a  launch    motor. 

132.  Adjustment  of  fuel  mixture  in  gas  and  oil  motors. 

CHAPTER  IX. 

SETTING  OR  TIMING  THE  VALVES  AND  IGNITER 200 

133.  Marks  for  valve  setting.  134.  Testing  valve  timing.  135.  Locating 
dead  centers  of  motor.  136.  Time  at  which  a  valve  should  open  and 
close.  137.  Marking  the  fly  wheel  for  valve  setting.  138.  Effect  of 
worn  and  loose  parts.  139.  Adjusting  the  ignition  timer.  140.  Com- 
paring the  time  of  ignition  in  different  cylinders. 

CHAPTER  X. 
TROUBLES,  REMEDIES  AND  REPAIRS 210 

141.  General.  142.  Conditions  that  cause  troubles  and  loss  of  power. 
143.  Backfiring.  144.  Misfiring.  145.  Pounding,  thumping,  or  ham- 
mering. 146.  Preignition  and  sharp  snaps  or  heavy  pounding. 
147.  Power  decreases  rapidly  at  a  uniform  rate.  148.  Power 
decreases  slowly.  149.  Erratic  behavior.  150.  Motor  does  not 
develop  full  power.  151.  Motor  runs  well,  then  loses  power  and 
cooling  water  heats  unduly. 

CHAPTER  XI. 
TESTS  OF  IGNITION  SYSTEMS 221 

152.  High-tension  (jump-spark)  system  with  induction  coils.  153.  High- 
tension  distributer  system  with  duplicate  batteries.  154.  High-tension 
magneto  system.  155.  Low-tension  arc-ignition  system.  156.  Test 
of  magneto  direct-current  electric  generator.  157.  Direct-current 
electro-magnetic  generator.  158.  Shuttle- wound  electric  generators. 
159.  Test  of  oscillatory  generators.  160.  High-tension  electric  gen- 
erators. 

CHAPTER  XII. 
TESTS  FOR  AIR  AND  GAS  LEAKS  IN  MOTOR 230 

161.  Examination  for  leaks  while  the  motor  is  running  in  service. 
162.  Running  tests  for  various  leaks.  163.  Hand  compression  tests 
for  leaks.  164.  Compressed-air  test.  165.  Hydrostatic  test. 


viii  CONTENTS 

CHAPTER  XIII.  PAGK 

CLEANING  AND  MISCELLANEOUS 235 

1 66.  Carbon  deposit  in  cylinder.  167.  Cleaning  the  spark  plug.  168.  Pit- 
ting and  warping  of  the  exhaust  valve.  169.  Regrinding  a  valve. 
170.  Running  the  motor  with  a  disabled  valve.  171.  Carbureter  re- 
pairs. Water-logged  float.  172.  Removing  frost  and  ice  from  the 
carbureter.  173.  Pipe  stoppages  by  gaskets  and  loose  hose  linings. 
174.  Cracked  cylinder  or  cylinder  head.  175.  Leaky  piston.  Scored 
cylinder.  176.  Care  and  handling  of  combustibles.  Removing  water. 

CHAPTER  XIV. 
INDICATOR  CARDS  FROM  PRACTICE 245 

177.  General.  178.  Indicator  cards  representing  American  practice. 
179.  Diagrams  showing  abnormal  pressures.  180.  Incorrect  valve 
setting  as  shown  by  the  diagram.  181.  Momentary  back  pressure. 
182.  Variation  of  time  of  ignition  as  shown  on  card.  183.  Dilute  mix- 
ture effect  on  card.  184.  Variation  of  compression  effects.  185.  Speed 
variation  effects  on  diagram. 


CHAPTER  XV. 

ECONOMY   AND   EFFICIENCY 276 

186.  Units  of  heat  energy  and  mechanical  energy.  187.  Motor  economy 
defined.  188.  Motor  efficiency  defined.  189.  Impulse-output  effi- 
ciency. 190.  Mechanical  efficiency.  191.  Thermodynamic  or  ther- 
mal efficiency.  192.  Plant  economy  and  efficiency.  193.  Compari- 
son of  efficiencies. 

CHAPTER  XVI. 

PHYSICAL  PROPERTIES  OF  GASES.  . . . ; 284 

194.  Introductory.  195.  Density  and  weight  of  gases.  196.  Laws  of  a 
perfect  gas.  197.  Example.  198.  Specific  heat  of  gases.  199.  Ex- 
ample. 200.  Volumetric  specific  heat.  201.  Example. 


CHAPTER  XVII. 

COMBUSTION  AND  HEAT  VALUES 293 

202.  Combustion  and  change  of  specific  volume  due  to  combustion. 
203.  Complete  and  incomplete  combustion.  204.  Heat  of  combustion  is 
constant.  205.  Heat  value  or  calorific  power.  206.  Economy  and 
efficiency  of  motor  as  affected  by  calorimeter  determinations  of  heat 
values.  207.  Higher,  or  effective,  heat  values.  208.  Higher  heat 
values  of  hydrogen.  209.  Lower  heat  values.  210.  Illuminants. 
211.  Saturated  and  unsaturated  hydrocarbons.  212.  Physical  form  of 
hydrocarbons.  213.  Dissociation  of  chemical  compounds.  214.  Com- 
bustion pressures  and  temperatures.  215.  Rate  of  flame  propagation 
and  combustion.  216.  Unusual  pressures  of  combustion.  217.  Over- 
rich  mixture.  218.  Moisture  in  air  and  gas.  219.  Gas  analyses  rela- 
tive to  moisture. 


CONTENTS  ix 

CHAPTER  XVIII.  PAGE 

FUELS  AND  GAS  MAKING 326 

220.  General.  221.  Retort  gas.  222.  Air  gas.  223.  Water  gas.  224.  Pro- 
ducer gas.  225.  Suction  producer.  226.  Theoretical  case  of  gas 
producer.  227.  Computations  for  theoretical  gas  producer.  228.  Com- 
parative heat  losses  for  burning  carbon  to  CO  or  CO2.  229.  Fuels 
for  continuous  suction  producers.  230.  Pressure  gas  producers  for 
continuous  operation.  231.  Down-draught  continuous  producer. 
232.  Under-feed  continuous  producer.  233.  Air-and-carbon  dioxide 
continuous  process.  234.  Combined  pressure  and  suction  producer. 
235.  Miscellaneous  types  of  producers.  236.  Intermittent  gas-making 
processes.  237.  Twin  producers.  238.  Blast-furnace  gas.  239.  Coke- 
oven  gas.  240.  Oil  gas  from  petroleum.  241.  Gasoline  gas  or  car- 
bureted air.  242.  Tar  destruction.  243.  Variation  in  quality  of 
producer  gas.  244.  Observation  of  quality  of  gas  from  a  producer. 
245.  Continuous  calorimeter  tests  of  gas.  246.  Efficiency  bases  of  gas 
producers. 

CHAPTER  XIX. 

PRESSURE-VOLUME  DIAGRAMS 367 

247.  Equations  for  work.  248.  Pressure-volume  diagram  for  complete 
cycle.  249.  Indicator  diagrams. 

CHAPTER  XX. 

THEORETICAL  HEAT  CYCLES 374 

250.  Assumption  for  theoretical  cycles.  251.  Notation.  252.  Addi- 
tional laws  of  a  perfect  gas.  253.  Relation  between  specific  heat  of 
constant  pressure  and  of  constant  volume.  254.  Thermodynamic 
changes.  255.  Isometric  change.  256.  Isobaric  change.  257.  Iso- 
thermal change.  258.  Adiabatic  change.  259.  Comparison  of  ex- 
pansion and  compression  lines.  260.  Theoretically  perfect  Otto  cycle. 
261.  Equations  for  Otto  cycle.  262.  Efficiency  as  affected  by  varia- 
tion of  compression.  263.  Effect  of  variation  of  specific  volume  on 
account  of  combustion.  264.  Effect  of  different  specific  heats  of 
charge  and  products.  265.  Effect  of  change  of  ratio  of  specific  heats 
by  combustion.  266.  Effect  of  imperfect  gas.  267.  Other  causes 
that  modify  theoretical  cycle.  268.  Modified  theoretical  Otto  cycle. 
269.  Theoretical  Brayton  cycle.  "270.  General  equations  for  thermo- 
dynamic  change.  271.  Other  thermodynamic  cycles. 

CHAPTER  XXI. 
RESULTS  OF  TRIALS 404 

272.  Introductory.  273.  United  States  Government  tests.  274.  Test  of 
a  5oo-horsepower  gas-engine  plant. 

CONVERSION  TABLES 432 


OF  THE 

UNIVERSITY 

OF 


THE   GAS   ENGINE 


CHAPTER  I. 

TYPES  OF  MOTORS,  IMPULSE  FREQUENCY,  SCAVENGING, 
REVERSING. 

i.  Introductory.  —  In  the  operation  of  the  internal-combustion 
motor  of  the  reciprocating  piston  type,  fuel  is  rapidly  burned,  or 
exploded,  in  an  enclosed  space,  and  the  increase  of  pressure 
thus  produced  is  utilized  to  drive  out  a  piston  which  is  connected 
more  or  less  directly  to  a  crank  shaft,  so  that  the  energy  of  com- 
bustion is  transmitted  to  the  latter  in  such  a  manner  as  to  cause 
it  to  rotate  and  have  capacity  to  deliver  power  for  the  performance 
of  useful  work. 

In  nearly  all  of  the  smaller  internal-combustion  motors,  a 
single  piston  reciprocates  in  the  round  bore  of  a  cylindrical  part, 
the  cylinder,  which  is  closed  at  one  end,  completely  and  per- 
manently in  some  types,  and  in  other  types  is  pierced  with  ports 
for  the  admission  of  the  charge  and  the  expulsion  of  the  gaseous 
products  of  combustion.  These  ports  are  intermittently  closed 
by  valves.  The  end  of  the  cylinder  next  the  crank  shaft  is  left 
open.  In  such  a  construction  the  piston  is  long,  of  the  type 
called  a  "trunk  piston." 

In  modern  designs  the  enclosed  space  at  the  end  of  the  cylinder 
and  into  which  the  piston  does  not  enter  is  called  the  "  com- 
bustion chamber."  The  name  "  compression  space "  is  also 
applied  to  it  for  the  reason  that,  in  modern  practice,  a  cylinderful 
of  combustible  mixture  is  compressed  into  it  before  burning. 

There  are  several  modifications  of  and  variations  from  this 
simple  form  of  motor,  the  more  important  of  which  will  be  con- 
sidered later. 


2  THE   GAS  ENGINE 

The  parts  of  the  motor  with  which  the  hot  gases  come  in  con- 
tact receive  considerable  heat  from  the  gases.  Unless  some 
means  is  provided  for  cooling  these  parts,  they  become  too  hot 
for  satisfactory  operation.  This  applies  especially  to  the  parts 


FIG.  1. 

Section  of  Single-Cylinder,  Single-Acting,  Four-Cycle  Motor  with  Diagrammatic 
Arrangement  of  Carbureter  and  Ignition  System. 

The  float  in  the  carbureter  reservoir  has  a  needle  valve  at  the  top  which  closes  the 
opening  of  the  gasoline  supply  pipe  when  the  float  rises  and  maintains  a  constant 
level  of  the  gasoline  lower  than  the  spray  nozzle  in  the  air  passage. 

The  gear  on  the  cam  shaft  is  twice  the  diameter  of  its  mate  on  the  crank  shaft,  so 
that  the  cam  shaft  rotates  at  half  the  speed  of  the  crank  shaft.  The  cam  lifts 
the  exhaust  valve  and  holds  it  open  during  every  second  upstroke  of  the  piston. 

The  rotor  of  the  timer  is  on  the  cam  shaft  and  closes  the  battery  circuit  every  second 
revolution  of  the  crank  shaft. 


TYPES  OF  MOTORS 


enclosing  the  combustion  chamber  and  the  port  through  which 
the  spent  gases  pass  out  from  the  motor  cylinder. 

In  small  motors,  some  are  cooled  by  water,  some  by  oil,  and 
some,    a    minor    number,    by    air. 
Large  motors  are  always  water  or 
oil  cooled. 

When  water  or  oil  is  used  for 
cooling,  a  jacket  of  the  cooling 
liquid  surrounds  the  combustion 
chamber  more  or  less  completely, 
and  also  part  of  the  bore  of  the 
cylinder.  The  water  or  oil  is  circu- 
lated through  the  jacket  space  in 
most  designs.  In  some  it  is  not  circulated. 


FIG.  2. 
Piston.     Trunk  Type. 


FIG.  3. 
Piston  Rings. 

The  larger  ring  shows  a  cut  to  allow 
the  ring  to  expand  against  the  cylin- 
der wall  to  make  a  tight  fit.  The  joint 
at  the  cut  is  made  so  that  the  sur- 
faces parallel  to  the  ends  of  the  ring 
bear  together  to  make  the  joint  tight. 
The  ring  must  be  sprung  together 
somewhat  to  fit  the  cylinder  bore. 


In  very  large 
motors  the  piston  and  exhaust 
valve  are  also  water-cooled. 

Air-cooled  motors,  always 
small  in  size,  have  projecting 
metallic  lugs,  fins,  or  other 
forms  with  which  the  air  comes 
in  contact.  Some  device,  such 
as  a  fan,  is  generally  used  to 
circulate  the  air  against  the 
cooling  parts,  but  sometimes 
only  the  motion  of  the  motor 
through  the  atmosphere,  as  on 
an  automobile,  is  depended  on 
to  bring  fresh  air  in  contact 
with  the  cooling  parts.  Some- 
times the  cylinder  is  encased, 
or  air-jacketed,  and  a  current 
of  air  forced  through  the  jacket 


space. 

Gas  turbines  have  been  constructed  and  tested  in  various 
forms,  but  none  has  yet  proved  successful.  The  efficiencies 
obtained  have  been  extremely  low.  In  some  cases  the  motor, 
of  the  steam  turbine  type,  would  not  develop  enough  power 


THE   GAS  ENGINE 


to  drive  the  compressor  for  precompressing  the  air  for  com- 
bustion. Pulverized  coal  for  fuel  has  been  tested  among 
others. 

Combustion,  as  used  in  connection  with  internal-combustion 
motors,  means  the  chemical  union  of  hydrogen,  carbon,  and 
hydrocarbons  of  the  fuel  with  the  oxygen  of  the  atmosphere, 
except  in  specific  cases  where  pure  oxygen,  unmixed  with 
any  other  chemical  element,  is  taken  as  the  supporter  of 
combustion. 

The  fuel  is  the  mechanical  mixture,  chemical  compound,  or 
element  that  combines  more  or  less  completely  with  the  oxygen 
during  combustion. 

There  is  a  certain,  although  quite  wide,  limit  to  the  propor- 
tions of  fuel  and  air  in  a  mixture  that  can  be  ignited  and  burned 

in  an  internal-combustion  motor; 
and  there  is  a  very  limited  range  of 
the  proportions  of  air  and  fuel  that 
will  give  the  maximum  or  nearly  the 
maximum  amount  of  power  from  the 
fuel  and  produce  clean  and  complete 
combustion. 

A  saturated  mixture  of  air  and  fuel 
cannot  be  burned  in  the  cylinder  of 
a  motor.  Air  is  saturated  with  the 
vapor  of  liquid  fuel  when  it  has 
assimilated  all  that  it  can,  which  is 
a  definite  amount.  It  is  in  a  way 
analogous  to  the  dissolving  of  salt 
in  water.  When  the  water  has  dis- 
solved a  certain  amount,  it  becomes 
saturated  and  will  not  dissolve,  or 
take  into  solution,  any  more  of  the  salt. 

Numerous  methods  of  mixing  the  fuel  with  air  and  burning  it 
have  been  tried  commercially  with  more  or  less  success.  In 
some  the  mixture  is  made  by  bringing  the  fuel  and  air  together, 
without  burning,  just  before  they  enter  the  cylinder  and  while  on 
their  way  to  it.  By  this  method  there  is  never  any  dangerous 


FIG.  4. 
Valve  and  Closing  Spring. 


TYPES   OF  MOTORS  5 

amount  of  the  combustible  mixture  on  hand.  In  qther  methods 
the  fuel  is  injected  into  the  combustion  chamber  after  the  latter 
is  filled  with  air.  In  still  others  the  mixture  is  made  in  quantity 
outside  the  combustion  space  and  then  forced  into  it.  In  some 
of  the  early  types  of  motors  the  air-and-gas  or  air-and-vapor 
mixture  is  drawn  into  the  cylinder  by  suction  and  ignited  at  about 
atmospheric  pressure.  It  was  found  later  that  greater  economy 
of  fuel  and  more  power  could  be  obtained  from  a  given  size  of 
cylinder  by  compressing  the  charge  before  igniting  it.  All 
modern  internal-combustion  motors  operate  either  by  com- 
pressing the  charge  of  combustible  mixture  before  ignition  or  by 
compressing  the  air  and  then  injecting  the  fuel,  in  this  case 
liquid,  into  the  compressed  air. 

The  cycle  on  which  the  internal-combustion  motor  operates 
is  the  principal  means  of  distinguishing  one  type  from  others. 
Cycle,  in  this  use,  means  the  series  of  changes  through  which 
each  charge  of  combustible  mixture  passes  from  the  time  any 
process  of  change  of  volume,  pressure,  or  chemical  action  begins 
on  it  until  it  passes,  or  is  free  to  pass,  out  of  the  motor.  The 
cycle  of  a  single-acting,  single-cylinder  motor  such  as  described 
above  is  not  changed  by  the  addition  of  cylinders  that  are  dupli- 
cates of  the  first  in  their  action  on  the  charge.  Neither  is  the 
cycle  changed  by  making  the  motor  double  acting  so  that  the 
piston  receives  an  impulse  to  drive  it  first  in  one  direction  and 
then  in  the  other,  provided  all  the  charges  are  acted  on  in  the 
same  manner. 

2.  Beau  de  Rochas-  or  Otto-Cycle  Motors.  —  In  motors 
approaching  the  theoretical  Otto  cycle  most  closely  a  charge  of 
combustible  mixture  in  the  gaseous  state  and  at  a  pressure  some- 
what less  than  atmospheric  is  taken  into  the  cylinder,  then 
compressed  into  the  combustion  chamber  by  the  instroke  of  the 
piston  and  ignited  at  about  the  time  the  compression  stroke  is 
completed.  (Ignition  may  occur  slightly  before,  at,  or  slightly 
after  the  completion  of  the  compression  stroke.)  Combustion 
takes  place  at  nearly  constant  volume,  accompanied  by  increase 
of  temperature  and  pressure.  The  increased  pressure  forces 
the  piston  out,  and  the  temperature  and  pressure  drop  on  account 


THE  GAS  ENGINE 


FIG.  6. 

Section  through  Combustion  Chamber  and  Ports  of   Single-Cylinder,  Four-Cycle, 
Water-Cooled  Gasoline  Motor.     Horizontal  Stationary  Type. 

1.  Cylinder  bore. 

2.  Inlet  valve. 

3.  End  of  lifting  arm  for  inlet  valve. 

4.  Closing  spring  for  inlet  valve. 

5.  Exhaust  valve. 

6.  End  of  lifting  arm  for  exhaust  valve. 

7.  Closing  spring  for  exhaust  valve. 

8.  Priming  valve  with  measuring  cup  for  introducing  gasoline  into  combustion 

space  for  starting  motor  when  very  cold. 

9.  Compression  relief   valve   located   part  way   down  barrel   of   cylinder.     For 

partially  relieving  compression  when  starting  by  hand, 
lo.    Movable  portion  of  contact   (low  tension)    igniter  surrounded   by   graphite 

bearing  (not  insulated), 
it.   Mixture  passage. 
12.   Cooling- water  space. 


TYPES  OF  MOTORS  7 

of  the  expansion.  An,  exhaust  port  is  opened  just. before  the 
end  of  the  stroke,  and  enough  of  the  products  of  combustion 
escape  in  the  gaseous  state  to  allow  the  pressure  in  the  cylinder 
to  fall  to  or  near  atmospheric.  This  completes  the  cycle,  although 
there  are  some  of  the  hot  gases  still  remaining  in  the  cylinder. 
The  remaining  gases  are  useless  in  performing  work,  for  they 
exert  no  appreciable  pressure  to  drive  the  piston  on  account  of 
having  direct  connection  with  the  atmosphere. 

The  method  of  removing  partly  or  completely  the  inert  gas  still 
remaining  in  the  cylinder,  and  of  introducing  another  charge 
of  combustible  mixture  is  not  a  part  of  the  real  cycle,  but,  since 
some  work  is  done  on  the  charge  before  its  introduction  into  the 
cylinder,  the  removal  of  the  products  of  combustion  and  the 
introduction  of  a  fresh  charge  must  be  considered  as  auxiliary 
to  the  real  cycle.  The  two  usual  methods  of  clearing  out  part  of 
the  inert  gases  of  combustion  (they  are  seldom  completely  cleared 
out)  after  they  have  fallen  to  atmospheric  pressure,  and  intro- 
ducing a  new  charge,  have  given  to  motors  operating  on  the  Otto 
cycle  the  names  by  which  they  are  commercially  known.  The 
two  types  are  designated  as  " four-cycle"  and  "two-cycle." 

The  "four-cycle"  motor  makes  an  exhaust  stroke  of  the  piston 
to  expel  part  of  the  gases  remaining  after  the  real  cycle  is  com- 
pleted, and  then  a  suction  stroke  to  draw  in  a  new  charge,  thus 
making  four  strokes  in  all  from  the  beginning  of  one  cycle  to  the 
beginning  of  the  one  that  succeeds  it. 

In  the  "two-cycle"  motor  the  elements  that  make  up  the  com- 
bustible charge  are  compressed  slightly,  either  together  or  sepa- 
rately, before  entering  the  motor  cylinder,  then  allowed  to  enter 
the  cylinder  and  drive  out  most  of  the  residual  gases  while  the 
piston  is  at  and  near  the  out  position.  The  inlet  and  exhaust 
ports  are  necessarily  open  simultaneously  during  this  operation. 
There  are  two  strokes  for  each  cycle. 

The  terms  "two-cycle"  and  "four-cycle"  are  indefinite  in 
themselves,  and  also  for  the  reason  that  they  can  be  applied 
respectively  to  any  motor  making  either  two  or  four  strokes  per 
cycle.  But  by  common  usage  they  have  a  definite  meaning  in 
reference  to  the  Otto-cycle  motor. 


THE  GAS  ENGINE 


TYPES  OF  MOTORS 


FIG.  6.     (See  also  Figs.  7  and  8.) 

Four-Cylinder,  Four-Cycle,  Air-Cooled  Automobile  Motor. 

The  H.  H.  Franklin  Manufacturing  Company,  Syracuse,  N.Y. 

1.  Cylinder. 

2.  Piston. 

3.  Piston  pin  (or  wrist  pin). 

4.  Connecting  red. 

5.  Crank  shaft. 

6.  Crank  case. 

7.  Inlet  valve,  hollow. 

8.  Exhaust  valve,  concentric  with  inlet  valve. 

9.  Auxiliary  exhaust  valve,  poppet  type. 

10.  Cam  for  lifting  auxiliary  exhaust  valve. 

11.  Cam  follower  for  auxiliary  exhaust  valve. 

12.  Lifting  rod  for  inlet  valve. 

13.  Lifting  rod  for  exhaust  valve. 

14.  Cam  for  opening  inlet  valve. 

15.  Cam  for  opening  exhaust  valve. 

16.  Closing  spring  for  inlet  valve. 

17.  Closing  spring  for  exhaust  valve. 

18.  Adjusting  screw  for  inlet  valve. 

19.  Adjusting  screw  for  exhaust  valve. 

20.  Inlet  pipe. 

21.  Exhaust  pipe. 

22.  Auxiliary  exhaust  pipe. 

23.  Cooling  flanges. 

24.  Timer.     Only  upper  part  shown. 

25.  Fan  for  cooling  the  cylinder. 

26.  Fly  wheel. 

27.  Starting  crank. 

28.  Oil  reservoir  for  lubricating  oil. 


10 


THE  GAS  ENGINE 


Gas-  and  Vapor-Burning  Motors. 

3.  Four-Cycle  Motors.  —  Motors  operating  approximately  on 
the  Otto  or  Beau  de  Rochas  cycle  and  making  four  single  strokes 
of  the  piston  for  each  cycle  are  commonly  known  as  "four-cycle'' 


30     31 


FIG.  7. 

(See  also  Figs.  6  and  8.) 
Four-Cylinder,  Four-Cycle,  Air-Cooled  Automobile  Motor. 

20.  Inlet  pipe.  25.    Fan  for  cooling  the  cylinder. 

21.  Exhaust  pipe.  29.   Magneto. 

22.  Auxiliary  exhaust  pipe.  30.    Rocker  arm  for  inlet  valve. 
24.    Timer.  31.    Rocker  arm  for  exhaust  valve. 

motors,  as  already  stated.  The  four  strokes  of  the  piston  corre- 
spond to  two  revolutions  of  the  crank  shaft  and  flywheel  in 
motors  resembling  in  general  appearance  the  ordinary  recipro- 
cating steam  engine. 


TYPES   OF  MOTORS 


II 


The  four-cycle  motor  of  the  usual  type  has  tw*o  ports  leading 
into  the  combustion  chamber;  one  through  which  the  combus- 
tible charge  of  mixed  air  and  gas,  or  air  and  vapor,  enters,  and 
the  other  through  which  the  inert  gases  remaining  after  com- 
bustion escape  after  expanding  against  the  out-moving  piston. 
Both  ports  have  valves  to  close  them.  When  permanent  gas 
under  pressure,  as  in  gas  mains  for  lighting,  is  used  for  fuel,  a 
fuel  valve  is  frequently  used  to  prevent  the  flow  of  gas  into  the 
air  passage  or  mixing  chamber  during  the  time  the  motor  is 
not  taking  in  a  charge. 

19 


FIG.  8. 

(See  also  Figs.  6  and  7.) 
Concentric  Inlet  and  Exhaust  Valves  for  Air-Cooled  Automobile  Motor. 


i.    Cylinder. 

7.  Inlet  valve,  hollow. 

8.  Exhaust  valve,  poppet  type,  con- 

centric with  7. 

12.  Lifting  rod  for  inlet  valve. 

13.  Lifting  rod  for  exhaust  valve. 


16.  Closing  spring  for  inlet  valve. 

17.  Closing  spring  for  exhaust  valve. 

18.  Adjusting  screw  for  inlet  valve. 

19.  Adjusting  screw  for  exhaust  valve. 
30.    Rocker  arm  for  inlet  valve. 

71.    Rocker  arm  for  exhaust  valve. 


12 


THE  GAS  ENGINE 


FIG.  9. 

Cross-Section    of    Motor    Cylinder    and    Valve    Chest,    showing    Valve-Lifting 

Mechanism. 


Valve. 

Collar  fastened  to  valve  stem. 

Cam  shaft,  lay  shaft  or  half-speed  shaft. 

Lobe  of  cam. 

Roller  follower  pressing  against  cam. 

7  and  lifted  by  cam  4  so  as  to  open  the  valve  i. 


i. 

2. 

3- 
4- 

5- 

6.  Rocker  arm  pivoted  at 

7.  Pivotal  support  for  6. 

8.  Cover  for  valve  chest. 

The  low-tension  ignition  points  (contact  points)  show  just  above  the  valve. 

The  intensity  of  compression  is  regulated  by  means  of  the  valve  chest  cover  8.     For 

natural  gas,  gasoline,  etc.,  the  almost  flat-bottomed  cover  shown  in  place  is  used. 

But  for  higher  compression,  as  for  producer  gas,  or  blast-furnace  gas,  a  cover 

with  a  projection  for  filling  the  space  between  the  cover  and  port  is  used.     See 

Fig.  10. 


TYPES  OF  MOTORS  13 

The  action  of  the  moving  parts  of  the  motor 'in  conjunction 
with  the  different  steps  of  the  heat  cycle  can  be  followed  by 
starting  with  any  of  the  events  that  occur.  It  is  convenient  to 
begin  with  the  suction  or  charging  stroke,  which  is  not  part  of 
the  heat  cycle. 

First  Stroke.  Four-Cycle  Motor.  —  Charging,  intake  or  suc- 
tion. The  piston,  starting  from  its  position  nearest  the  com- 
bustion chamber,  draws  in  a  charge  by  suction  during  the  out- 
stroke.  The  inlet  valve  either  opens  by  suction  automatically 
against  the  resistance  of  a  comparatively  weak  spring,  or  is 
opened  mechanically  against  a  fairly  strong  spring.  The  inlet 
valve  closes  at,  or  about,  the  completion  of  the  suction  stroke. 

Second  Stroke.  Four-Cycle  Motor.  —  Compression.  The 
piston,  returning  during  the  instroke,  compresses  the  charge  into 
the  combustion  chamber.  Both  the  inlet  and  exhaust  valves 
remain  closed  during  the  compression  stroke. 


FIG.  10. 

Covers  for  Valve  Chest  of  Fig.  9.     Covers  are  of  different  depths  to  give  different 
degrees  of  compression  according  to  the  fuel  used. 

The  compressed  charge  is  ignited  just  before,  at,  or  very 
slightly  after  the  completion  of  the  compression  stroke.  Ignition 
is  accomplished  by  an  electric  spark,  electric  arc,  a  flame,  or  a 
hot  piece  of  metal  or  other  substance. 

Third  Stroke.  Impulse  Stroke.  —  Completion  of  combustion, 
expansion.  Combustion,  producing  rise  of  both  temperature 
and  pressure,  is  generally  well  under  way  by  the  time  the  piston 
has  made  an  appreciable  part  of  the  stroke  following  compression. 
Combustion  is  completed  and  the  increased  pressure  drives  the 
piston  out,  allowing  expansion  of  the  gases  as  the  piston  moves. 
When  the  piston  is  well  toward  the  completion  of  the  impulse 
stroke,  the  exhaust  valve  is  mechanically  opened  against  the 


THE  GAS  ENGINE 


OH 

I 

I 


a  1 


Bfi 

a 

W 


O 


TYPES   OF  MOTORS  15 

pressure  of  the  gases  in  the  cylinder  and  of  a  stoyt  spring.  The 
hot,  inert  gases  partly  escape  by  expansion. 

Fourth  Stroke.  Four-Cycle  Motor.  —  Expulsion  of  inert  gases. 
The  exhaust  valve  is  kept  open,  and  the  piston,  moving  toward 
the  combustion  chamber,  expels  part  of  the  remaining  gases. 
The  exhaust  valve  then  closes  at,  or  more  generally  slightly 
after,  the  completion  of  the  exhaust  stroke. 

In  a  single-acting,  single-cylinder,  four-cycle  motor  operating 
on  the  Otto  cycle  and  having  the  piston  joined  directly  to  the 
crank  by  means  of  a  connecting  rod,  the  crank  receives  an  impulse 
only  once  in  two  revolutions.  This  necessitates  a  very  heavy  or 
large-diameter  fly  wheel  to  secure  reasonably  steady  running. 

4.  Auxiliary  Exhaust  Port.  —  In  a  small  proportion  of  four- 
cycle motors,  an  auxiliary  exhaust  port  is  provided  in  the  wall  of 
the  cylinder  where  it  is  uncovered  by  the  motion  of  the  piston 
just  before  the  completion  of  the  outstroke.    When  the  auxiliary 
port  is  thus  uncovered  just  before  the  completion  of  the  impulse 
stroke,  a  considerable  portion  of  the  burned  gases  escapes  through 
it  on  account  of  their  expansion.     By  opening  the  valve  of  the 
customary  exhaust  port  leading  out  from  the  combustion  cham- 
ber at  the  usual  time,  two  exhaust  passages  for  the  escape  of  the 
products  of  combustion  are  provided,  and  the  release  of  the  gases 
can  be  made  so  rapid  that  there  is  practically  no  back  pressure 
remaining  to  resist  the  motion  of  the  piston  at  the  moment  of 
beginning  its  exhaust  stroke.     The  auxiliary  port  is  again  covered 
by  the  piston  soon  after  the  beginning  of  the  exhaust  stroke,  and 
the  remaining  inert  gases  are  partly  expelled  by  the  motion  of 
the  piston,  the  gases  passing  out  through  the  port  in  the  com- 
bustion chamber. 

The  auxiliary  exhaust  port  has  a  valve  in  some  designs,  but 
none  is  used  in  others.  The  valve  is  sometimes  of  the  automatic 
check-valve  type  and  is  either  a  ball  resting  on  its  seat  by  its  own 
weight  only,  or  a  spring-closed  valve  similar  to  that  used  for  an 
automatic  inlet.  In  other  designs  a  mechanically  operated  valve 
is  used  in  the  auxiliary  exhaust  port. 

5.  Atkinson  Four-Cycle  Motor.  —  Some  years  ago  Mr.  Atkin- 
son, in    England,   constructed   a   single-cylinder,    single-acting, 


i6 


THE   GAS  ENGINE 


TYPES   OF  MOTORS  I/ 


FIG.  12.    (See  also  Fig.  13.) 

Two-Cylinder,  Four-Cycle,  Single-Acting,  Oil-Cooled  Motor  for  Traction  Engine. 

45  brake  horsepower. 

Adapted  to  burn  gasoline  or  cheap  grade  kerosene.     Electric  ignition. 
Hart-Parr  Company,  Charles  City,  Iowa. 

Section  through  axis  of  one  cylinder. 

Oil-jacketed  cylinder.     Cooling  oil  circulated  by  rotary  pump. 

Exhaust  jets  create  upward  blast  of  air  through  cooler  by  ejector  action.  Hori- 
zontal pipe  from  relief  (auxiliary)  exhaust  is  hidden  by  exhaust  pipe  from 
compression  end  of  cylinder. 

One  cam  operates  both  the  inlet  and  the  exhaust  valve  of  one  cylinder.  Cylinder 
barrel  and  breech  cast  in  one  piece. 

Removable  valve  cages  (with  valve  seats)  ground  to  fit  in  cylinder  casting. 

During  a  five-hour  continuous  test  of  this  motor  under  a  nearly  constant  average 
load  of  61.98  brake  (delivered)  horsepower  the  temperature  of  the  cooling 
oil  did  not  exceed  163°  F.,  with  a  maximum  atmospheric  temperature  of 


1 8  THE   GAS  ENGINE 

four-cycle  motor  operating  on  the  Otto  cycle,  in  which  the  crank 
made  only  one  revolution  for  every  four  strokes  of  the  piston. 
This  was  accomplished  by  means  of  a  somewhat  complicated 
system  of  links  and  other  parts.  The  crank  thus  received  an 
impulse  every  revolution.  The  piston  moved  farther  in  toward 
the  combustion  chamber  on  the  exhaust  stroke  than  on  the  com- 
pression stroke,  in  order  to  more  completely  free  the  cylinder 
from  the  inert  gases  of  combustion. 


FIG.  13. 

(See  also  Fig.  12.) 

Two-Cylinder,  Four-Cycle,  Oil-Cooled  Motor  for  Traction  Engine,  Unmounted. 
45  horsepower.  Adapted  to  burn  gasoline  or  cheap  grade  kerosene.  Hart-Parr 
Company,  Charles  City,  Iowa. 

The  motor  operated  economically  with  regard  to  fuel  con- 
sumption, and  had  good  speed  regulation,  but  the  lack  of  mechan- 
ical balance  of  the  moving  parts  was  so  serious  a  feature  as  to 
prevent  its  commercial  adoption  to  any  great  extent. 


TYPES  OF  MOTORS  19 

6.  "  The  Complete-Expansion  Gas  Engine. "  —  Figs.  64%,  to 
71.  This  is  made  as  a  four-cycle,  double-acting  tandem  engine. 
It  is  the  design  of  Mr.  C.  E.  Sargent,  and  has  several  unique 
features. 

When  operating  at  any  load  less  than  its  full  capacity,  air  only 
is  admitted  during  the  early  part  of  the  charging  stroke.  Then 
gas  also  is  admitted  at  a  time  determined  by  the  governor,  and 
continues  entering  until  both  air  and  gas  are  cut  off  before  the 
completion  of  the  charging  stroke.  At  full  load  gas  begins  to 
enter  at  the  same  time  as  the  air  (at  the  beginning  of  the  charging 
stroke)  and  both  are  cut  off  at  the  same  instant.  The  instant  of 
cutting  off  the  mixture  is  invariable  so  far  as  automatic  (governor) 
regulation  is  concerned,  and  is  timed  to  suit  the  kind  of  gas  used. 
The  range  of  setting  for  the  cut-off  is  from  five-eighths  to  three- 
quarters  of  the  stroke.  After  cutting  off,  the  charge  expands 
during  the  remainder  of  the  charging  stroke.  The  fixed  point 
of  cut-off  determines  the  extent  of  compression,  which  is  constant 
for  all  loads.  Since  producer  gas  can  be  compressed  more  with- 
out self-ignition  than  natural  gas,  the  point  of  cut-off  is  set  later 
for  the  former  than  for  the  latter.  The  heat  value  of  the  producer 
gas  mixture  is  less  than  that  of  the  natural  gas,  and  this  allows  a 
higher  compression  without  causing  a  higher  terminal  pressure 
at  the  end  of  the  impulse  (expansion)  stroke.  On  account  of 
cutting  off  the  charge  before  the  completion  of  the  charging 
stroke,  expansion  is  carried  out  further  during  the  impulse  stroke 
than  in  motors  which  admit  the  charge  (air  and  mixture)  during 
the  entire  intake  stroke.  The  pressure  at  the  time  of  opening 
the  exhaust  valve  is  well  down  toward  atmospheric,  hence  the 
name  "Complete-Expansion  Gas  Engine." 

The  cylinder  volume  is  about  twenty-five  per  cent  greater  than 
in  the  usual  types  of  four-cycle  motors  of  the  same  power,  but  it 
is  claimed  that  the  greater  cost  of  construction  on  this  account  is 
more  than  balanced  by  the  gain  in  economy  on  account  of  the 
more  complete  expansion. 

Another  feature  of  the  engine  is  that  there  is  only  one  port  into 
each  combustion  chamber,  which  is  unusual  for  either  four-cycle 
or  two-cycle  motors.  The  charge  enters  and  the  burned  gases 


20  THE   GAS  ENGINE 

escape  through  the  same  cylinder  port.  There  is  a  small  port 
with  a  by-pass  valve  for  balancing  the  pressure  on  the  poppet 
valve  that  closes  the  cylinder  port,  but  its  function  does  not 
include  allowing  the  burned  gases  to  escape.  The  by-pass  valve 
is  opened  by  cam  action  just  before  the  exhaust  is  to  take 
place. 

On  account  of  the  extent  to  which  the  expansion  is  carried  out, 
the  burned  gases  are  so  cool  at  the  time  the  exhaust  valve  opens 
that  it  is  not  necessary  to  water-cool  the  valve  as  in  the  usual 
types  of  large  gas  engines.  The  builders  of  the  engine  make 
the  following  statement  regarding  the  temperatures  of  the  burned 
gases: 

"  Aside  from  the  greater  economy  of  an  engine  which  expands 
the  charge  to  practically  atmospheric  pressure,  the  average  tem- 
perature during  the  cycle  is  less  and  the  engine  is  not  subjected 
to  the  internal  strains  indigenous  to  the  higher  temperatures,  — 
for  example,  the  initial  temperature  in  both  types  is  about  3000°  F., 
the  terminal  temperature  in  the  ordinary  engine  is  1800°  F.,  and 
in  the  complete-expansion  engine  500°  F.,  making  the  average 
temperature  of  the  working  stroke  of  the  former  2400°  F.  and  in 
the  complete-expansion  engine  1750°  F." 

The  theoretical  cycle  which  this  motor  approximates  is  shown 
in  Fig.  135. 

7.  The  Nuremberg  motor  in  large  sizes,  and  the  Gobron- 
Brillie  motor  in  small  sizes  for  automobile  and  similar  uses,  both 
four-cycle,  use  an  open-end  cylinder,  dispensing  with  cylinder 
heads.  There  are  two  pistons  to  one  cylinder.  The  pistons  are 
both  connected  to  the  same  crank  shaft  so  as  to  approach  and 
recede  from  each  other  and  the  middle  of  the  cylinder  simul- 
taneously. The  one  next  the  crank  shaft  has  a  connecting  rod 
of  the  usual  length  and  form.  The  rear  piston  has  a  crosshead 
at  the  end  of  the  cylinder  farthest  from  the  crank  shaft,  and  the 
crosshead  is  connected  to  the  crank  shaft  by  two  connecting  rods, 
one  on  each  side  of  the  cylinder  (or  cylinders).  The  cranks  for 
the  two  pistons  of  one  cylinder  are  at  180  degrees  with  each  other, 
or,  expressed  otherwise,  directly  opposite  each  other.  The  ports 
are  several  small  openings  arranged  circumferentially  around 


TYPES   OF  MOTORS 


21 


the  middle  of  the  cylinder.     The  inlet  and  exhaust  through  these 
ports  are  controlled  by  valves  in  the  usual  manner. 

This  construction  removes  what  is  sometimes  a  source  of 
serious  trouble  in  large  gas  engines,  that  is,  the  fracture  of  the 
cylinder  heads  by  heating  and  unequal  expansion.  There  are 
no  glands  or  stuffing  boxes  required  for  piston  rods. 


FIG.  14. 

Open-End  Cylinder  Motor.     Longitudinal  sections  at  right  angles  to  each  other. 

Four-cycle.     Two  cylinders.     Two  pistons  in  each  cylinder.     Inlet  and  exhaust 

ports  at  middle  of  cylinder. 
The  two  pistons  in  each  cylinder  approach  each  other  during  compression,  and 

recede  from  each  other  during  the  impulse  or  expansion  stroke.     One  impulse 

every  revolution  in  the  two-cylinder  motor. 

8.  Two-Cycle  Motors.  —  This  name  is  generally  applied  to 
motors  operating  on  the  Otto  cycle,  and  in  which  each  piston 
makes  only  two  strokes  for  each  impulse  it  receives  in  a  single- 
acting  motor. 

The  two-cycle  motor,  in  its  simplest  and  most  usual  form,  has 
its  inlet  and  exhaust  ports  in  the  walls  of  the  cylinder  bore  near 
the  end  farthest  from  the  combustion  chamber.  Its  action  can 


22  THE  GAS  ENGINE 

be  followed  by  starting  with  the  piston  in  its  position  nearest  the 
combustion  chamber,  and  a  compressed  charge  in  the  latter. 

First  Stroke.  Two-Cycle  Motor.  —  The  compressed  charge 
is  ignited  and  burned,  and  the  consequent  increased  pressure 
drives  the  piston  outward  as  the  charge  expands.  At  the 
beginning  of  the  outstroke  the  enclosed  crank  case  is  full  of 
combustible  mixture  previously  drawn  in.  The  outstroke  com- 
presses this  to  some  extent.  When  the  piston  is  well  toward  the 
completion  of  the  outstroke,  it  uncovers  a  row  of  small  exhaust 
port-holes  that  pierce  the  cylinder  walls  and  extend  somewhat 
less  than  half  way  around  it  circumferentially.  This  allows  part 
of  the  products  of  combustion  to  escape  by  expansion.  The 
piston,  continuing  its  outstroke,  next  uncovers  a  similar  row  of 
inlet  port -holes  that  connect  to  the  crank  case.  This  allows  a 
charge  of  the  slightly  compressed  combustible  mixture  in  the 
crank  case  to  flow  into  the  cylinder  and  drive  out  most  of  the 
remaining  inert  gases. 

Second  Stroke.  Two-Cycle  Motor. —  The  piston,  now  returning 
toward  the  combustion  chamber,  covers  first  the  inlet  port-holes, 
then  the  exhaust  port-holes,  and  then  compresses  the  charge  till 
the  end  of  the  instroke  is  reached.  During  the  instroke  the 
piston  also  draws  more  mixture  into  the  crank  case  by  suction. 

The  mixture  enters  the  crank  case  generally  either  through  an 
automatic  poppet  valve  in  or  near  its  walls  or  through  a  port  in 
the  bore  of  the  cylinder  that  is  uncovered  when  the  piston  has 
nearly  completed  its  compression  stroke  (instroke).  The  latter 
port  connects  the  crank  case  to  the  source  of  fuel  and  air  supply. 
A  motor  constructed  in  the  latter  manner  has  no  valves,  and  need 
have  no  moving  parts  but  the  piston,  connecting  rod,  crank  shaft, 
and  the  parts  rigidly  connected  to  them.  This  does  not  include 
the  ignition  system.  This  great  simplicity  makes  this  style  of 
motor  at  once  attractive  on  account  of  small  cost  of  construction 
and  absence  of  numerous  parts  to  wear  and  get  out  of  repair. 
There  are  certain  features  of  its  operation,  however,  that  have 
prevented  its  adoption  to  as  great  an  extent  as  the  four-cycle 
motor.  While  it  seems  at  first  thought  that  the  power  developed 
per  pound  of  weight  of  motor  should  be  much  more  in  the  two- 


TYPES  OF  MOTORS 


FIGS.  15  AND  16. 
Two-Cycle,  Valveless,  Three-Port  Motor. 


Longitudinal  sections. 


6.  Exhaust  port. 

7.  Baffle  plate. 

Fine-mesh    wire    screen    to    prevent 

back  firing  into  the  crank  case. 
Spark  plug. 


8. 


Cylinder. 
Piston. 
Crank  case. 
Inlet  to  crank  case. 
5.    Passage  from  crank  case  to  inlet  port 

of  combustion  chamber. 

In  Fig.  1 6  the  piston  has  just  completed  the  compression  stroke  (upstroke  in  this 
case)  and  uncovered  the  inlet  port  4  to  the  crank  case  and  mixture  is  flowing  into 
the  latter  on  account  of  the  partial  vacuum  created  in  it  by  the  upward  movement 
of  the  piston. 

Fig.  15  shows  the  piston  after  the  charge  has  been  burned  and  the  piston  moved 
down  to  the  lower  end  of  its  stroke.  The  burned  gases  are  passing  out  through 
the  exhaust  port  6  and  the  compressed  mixture  in  the  crank  case  is  flowing  into 
the  combustion  space.  The  baffle  plate  7  deflects  the  entering  charge  upward 
so  that  it  does  not  pass  out  of  the  exhaust  port. 


24  THE   GAS  ENGINE 

cycle  than  in  the  four-cycle  motor,  each,  in  fact,  develops  about 
the  same  amount  of  power  per  pound  of  weight. 

When  a  two-cycle  motor  of  the  simple  single-acting  form  just 
mentioned  is  changed  to  double-acting  (with  both  ends  of  the 
cylinder  closed  as  in  most  steam  engines,  and  a  combustion 
chamber  at  each  end  of  the  cylinder)  it  becomes  impossible  to 
initially  compress  in  the  crank  case  all  the  combustible  mixture 
in  order  to  force  it  into  the  combustion  cylinder.  The  double- 
acting  two-cycle  motor  therefore  requires  an  additional  cylinder 
for  the  initial  compression  of  the  charge.  Numerous  designs  of 
double-acting  two-cycle  motors  have  been  operated.  In  some 
the  fuel  and  air  are  mixed  on  their  way  to  the  compression 
cylinder,  as  in  the  case  of  the  single-acting  motor,  while  in  others 
the  air  is  compressed  in  one  auxiliary  compression  cylinder,  and 
the  gas,  or  a  mixture  of  fuel  vapor  and  air,  too  rich  in  combustible 
matter  to  burn,  is  compressed  in  another  auxiliary  cylinder,  and 
the  contents  of  the  two  auxiliary  cylinders  are  mixed  as  they  pass 
into  the  combustion  cylinder.  By  this  means  there  is  no  appre- 
ciable amount  of  combustible  mixture  ever  on  hand  outside  of 
the  combustion  cylinder.  The  liability  to  dangerous  explosions 
outside  of  the  combustion  cylinder,  which  must  be  carefully 
considered  for  large  motors,  is  thus  eliminated. 

9.  The  Koerting  Two-Cycle  Motor  is  of  the  double-acting  type, 
with  separate  auxiliary  compression  cylinders  for  air  and  gas. 
Large  motors  of  this  type  have  been  put  into  practical  operation 
extensively  both  in  this  country  and  Europe.  Many  of  them 
have  been  designed  especially  for  using  blast-furnace  gas. 

The  Koerting  motors,  double-acting,  are  constructed  with  an 
inlet  port  leading  into  each  combustion  chamber  and  an  exhaust 
port  composed  of  a  great  number  of  small  holes  that  pierce  the 
cylinder  wall  circumferentially  at  the  middle.  The  piston  has  a 
length  but  slightly  less  than  that  of  the  stroke.  It  covers  the 
exhaust  port  except  when  near  the  end  of  its  stroke  in  either 
direction.  The  same  port  is  thus  used  for  exhausting  alternately 
from  both  ends  of  the  cylinder.  After  the  exhaust  port  has  been 
uncovered  and  the  inert  gases  have  escaped  till  the  pressure  in 
the  combustion  cylinder  has  fallen  to  about  that  of  the  atmos- 


TYPES   OF  MOTORS 


FIG.  17. 

Koerting  Two-Cycle,  Double-Acting  Gas  Engine. 
Diagram  showing  the  arrangement  of  parts. 

1.  Combustion  cylinder. 

2.  Piston,  drum  type. 

3.  Gas  pump.     Piston  at  left  end. 

4.  Air  pump.'    Piston  at  left  end. 

5.  Air  duct  to  inlet  valve. 

6.  Gas  duct  to  inlet  valve. 

7.  Inlet  valve. 

8.  Exhaust  passage  connecting  to  several  small  ports  around  the  middle  of  the 

cylinder. 

9.  Air  valve  at  pump. 
10.    Gas  valve  at  pump. 

The  opening  and  closing  of  the  inlet  valves  7  do  not  vary  either  in  time  or  extent. 
One  of  the  inlet  valves  opens  after  the  piston  has  moved  away  from  it  and 
uncovered  the  exhaust  ports.  The  time  and  stroke  of  the  air-pump  piston  and 
gas-pump  piston  do  not  vary.  When  the  inlet  valve  of  the  combustion  chamber 
opens,  air,  which  has  been  compressed  by  the  air  pump,  flows  into  the  combus- 
tion cylinder.  The  piston  of  the  air  pump  continues  its  compression  stroke 
during  this  time.  The  governor  controls  the  time  at  which  gas,  compressed  by 
the  gas  pump,  begins  to  flow  into  the  combustion  cylinder  with  the  air.  The 
gas  and  air  mixture  then  continues  to  flow  in  till  the  inlet  valve  closes.  The  motor 
piston  2  is  near  the  exhaust  end  of  its  stroke  during  the  intake  of  charge.  The 
process  is  then  repeated  for  the  opposite  end  of  the  combustion  cylinder.  The 
piston  receives  an  impulse  each  stroke. 


26  THE   GAS  ENGINE 

phere,  the  air  inlet  port  is  opened  and  air  rushes  in  to  scavenger 
the  cylinder  by  driving  out  the  remaining  inert  gases.  If  any  of 
the  air  passes  out  of  the  exhaust  port,  there  is  no  loss  of  fuel  such 
as  occurs  if  too  much  combustible  mixture  is  brought  in  as  in 
other  types  of  two-cycle  motors.  After  part  of  the  compressed 


PLAN 


ELEVATION 
FIG.   18. 

Koerting   Two-Cycle,    Double-Acting   Gas   Engine.     Single   cylinder.     Plan   and 

elevation.     Made  in  units  (single-cylinder)  from  400  to  1500  horsepower. 

i.    Motor  cylinder.  3.    Gas-pump  cylinder. 

4.    Air-pump  cylinder. 

The  overhanging  crank  on  the  side  opposite  the  flywheel  is  f<?r  driving  the  air  pump 
and  gas  pump.     The  main  connecting  rod  (for  the  motor  piston)  is  not  shown. 

air  has  passed  from  the  auxiliary  cylinder  into  the  combustion 
cylinder,  the  fuel  inlet  valve  is  opened,  and  the  gas  and  remaining 
air  mix  as  they  pass  into  the  combustion  cylinder.  Special  forms 


TYPES   OF  MOTORS  27 

of  port  openings  are  adopted  to  cause  the  mixture^to  enter  in  such 
a  way  as  to  remain  in  and  near  the  compression  space,  while  the 
air  that  is  not  mixed  with  the  fuel,  but  still  remains  in  the  com- 
bustion cylinder,  stays  next  to  the  piston  head.  This  stratifica- 
tion of  the  contents  of  the  combustion  cylinder  is  thought  to  give 
better  economic  results  than  other  methods,  and  allows  the  use 
of  very  lean  (low  in  capacity  to  produce  heat)  fuel,  while,  at  the 
same  time,  the  speed  can  be  controlled  by  regulating  the  amount 
of  fuel  that  enters  for  any  stroke. 

10.  Brayton  Motor  and  Cycle.  —  This  cycle  was  invented  by 
Mr.  Brayton  of  Philadelphia,  and  a  motor  operating  on  it  was 
constructed  in  1873.  The  air  and  fuel  were  compressed  by 
auxiliary  compressors  and  delivered  into  separate  tanks  at  a 
pressure  somewhat  greater  than  that  of  the  maximum  in  the 
combustion  cylinder.  They  were  then  allowed  to  flow  toward 
the  combustion  cylinder  and  mix  together  just  before  entering  it. 
The  mixture  then  passed  through  a  fine-mesh  wire  screen  that 
guarded  the  port,  and  burned  immediately  after  passing  through 
the  screen.  The  latter  was  to  prevent  the  flame  from  backfiring 
into  the  port.  The  mixture  was  admitted  to  the  combus- 
tion cylinder  just  as  the  piston  was  ready  to  start  on  the  out- 
stroke,  and  burned  at  a  uniform  pressure,  practically  the  same 
as  that  in  the  tanks.  The  piston  was  forced  out  by  the  pressure, 
and  the  mixture  was  admitted  during  one-third  of  its  stroke,  more 
or  less,  and  then  the  inlet  valve  closed  and  the  highly  heated 
contents  of  the  cylinder  expanded  to  drive  the  piston  out  to  nearly 
the  end  of  the  stroke,  when  the  exhaust  valve  opened  and  allowed 
them  to  escape  till  the  pressure  fell  to  about  atmospheric.  On 
the  return  stroke  the  residual  gases  in  the  combustion  cylinder 
were  compressed  by  the  piston  to  nearly  the  same  pressure  as  that 
of  the  fuel  and  air  tanks.  A  small  by-pass  at  the  inlet  valve 
allowed  enough  mixture  to  enter  the  combustion  cylinder  to  keep 
a  small  pilot  flame  going  constantly  at  the  wire  screen.  This 
flame  ignited  the  charge  as  soon  as  it  began  to  enter  the  cylinder. 

The  cycle  of  the  gases  in  the  Brayton  motor  is  accomplished 
partly  in  the  air  and  fuel  compression  cylinders,  and  the  remainder 
in  the  combustion  cylinder. 


28  THE   GAS  ENGINE 

Theoretically  the  Brayton  cycle  is  of  such  a  nature  as  to 
deserve  careful  consideration  with  a  view  to  its  commercial 
application.  The  chief  difficulties  that  the  inventor  states  he 
met  in  the  motors  constructed  to  operate  on  it  were  with  the  wire 
gauze  screen  and  other  devices  used  to  prevent  back  firing,  and 
from  the  extinguishing  of  the  pilot  flame  and  consequent  stoppage 
of  the  motor.  Many  devices  in  addition  to  the  wire  gauze  were 
tried  without  entire  success  in  any  case.  The  addition  of  air  and 
gas  compressors  may  seem  a  serious  objection  to  this  motor  in 
comparison  with  the  simpler  ones  for  operating  on  the  Otto  cycle. 
Yet  it  is  to  be  remembered  that  the  larger  Otto-cycle,  two-cycle 
motors  (Koerting  motors)  have  auxiliary  compressors  for  the  air 
and  the  fuel.  The  absence  of  high  pressures  of  explosion  in  the 
Brayton  motor  is  well  worthy  of  consideration,  especially  for 
very  large  motors.  A  central  compressor  plant  for  supplying 
compressed  air  and  fuel  to  several  motors  would  simplify  the 
equipment  of  a  power  plant. 

Oil-Burning  Motors. 

n.  In  the  motors  that  have  been  discussed  the  combustible 
charge  enters  the  cylinder  either  in  the  form  of  a  mixture  of  gas 
and  air  or  of  vapor  and  air.  There  is  another  class  of  internal- 
combustion  motors,  in  less  general,  but  extensive,  use,  whose 
fuel  is  injected  into  the  cylinder,  combustion  chamber,  or  an 
extension  of  the  latter,  in  liquid  form.  Kerosene  and  other  of 
the  less  volatile  distillates  of  petroleum  are  used,  and,  in  one 
or  two  designs,  even  the  crude  petroleum  itself  is  used  for  fuel. 
The  high  cost  of  kerosene  in  comparison  with  the  heavier  or 
less  refined  oils  is  the  chief  objection  to  its  use  in  large  motors. 

12.  The  Hornsby-Akroyd  Oil  Motor  has  a  somewhat  jug- 
shaped  hollow  metal  vaporizer  attached  by  the  neck  end  to  the 
end  of  the  combustion  cylinder  so  as  to  form  an  extension  of  the 
latter.  The  cylinder  otherwise  resembles  that  of  an  ordinary 
four-cycle,  single-acting,  Otto-cycle  motor.  The  vaporizer 
space  and  cylinder  space  are  joined  only  by  the  comparatively 
small  opening  of  the  neck  connection.  Inlet  and  exhaust  ports 


TYPES  OF  MOTORS 


29 


connect  with  the  combustion  chamber.  The  liquid  fuel  is 
injected  into  the  vaporizer  through  one  or  more  minute  nozzles 
so  that  it  enters  as  a  spray. 

The  vaporizer,  usually  of  cast  iron,  is  kept  at  a  dull-red  heat. 
Before  starting  the  motor,  the  vaporizer  is  heated  by  an  external 
flame,  but  after  the  motor  is  running,  the  heat  of  combustion 
inside  the  cylinder  and  vaporizer  keeps  the  latter  hot  enough. 


Cooling  Water 
Outlet 


FIG.  19.     (See  also  Figs.  20,  21,  22,  23,  24,  72.) 

Hornsby-Akroyd  Four-Cycle,  Single-Acting  Engine  for  Kerosene  and  Distillates. 
De  La  Vergne  Machine  Company,  New  York,  N.Y.  Longitudinal  section 
through  cylinder. 

Oil  is  injected  into  the  internally  ribbed  vaporizer  during  the  suction  stroke  and 
vaporized  by  the  heat  of  the  vaporizer.  The  compression  stroke  forces  the  air 
into  the  vaporizer  and  the  mixture  is  ignited  at  about  the  completion  of  the  com- 
pression stroke  by  the  heat  of  the  vaporizer. 

The  amount  of  fuel  oil  injected  is  controlled  by  a  governor  acting  on  a  by-pass 
valve  connected  to  the  outlet  passage  of  a  plunger  pump. 


30  THE   GAS  ENGINE 

The  operation  is  almost  exactly  the  same  as  that  of  a  four- 
cycle, Otto-cycle  gas  or  vapor  motor.  Taken  step  by  step,  it  is, 
dealing  with  the  strokes  of  the  piston : 

First  Stroke.  —  Charging,  intake  or  suction.  The  piston, 
starting  from  its  position  nearest  the  combustion  chamber,  draws 


FIG.  20. 
Transverse  Section  of  Hornsby-Akroyd  Oil  Engine. 

The  fuel-oil  pump  is  shown  at  the  bottom  of  the  figure,  and  the  governor  at  the 
right-hand  upper  part. 

in  air  to  an  amount  practically  equal  to  the  volume  of  displace- 
ment of  the  piston  during  its  outstroke.  Oil  is  forced  into  the 
vaporizer  during  all  or  part  of  the  outstroke,  and  vaporized 


TYPES   OF  MOTORS  31 

more  or  less  completely.  The  air  inlet  valve  opens  at  about  the 
time  of  beginning  the  stroke,  and  closes  at  or  about  the  end  of 
the  stroke. 


FIG.  21. 

Injector  Nozzle  Used  on  Hornsby-Akroyd  Oil  Engine. 

The  oil  enters  through  the  pipe  at  the  left  end,  passes  through  the  ball  check  valve 
and  around  the  helical  grooves  in  the  pin  or  plug  at  the  right  end,  where  it  escapes 
into  the  vaporizer. 

Second  Stroke.  —  Compression  and  completion  of  vaporization. 
The  piston,  returning  on  the  instroke  to  its  first  position,  com- 
presses the  air  and  oil  vapor.  If  any  of  the  oil  remains  unvapor- 
ized  at  the  beginning  of  this  stroke,  its  vaporization  is  completed 
during  the  early  part  of  compression.  The  compression  of  the 


Water  Outlet 


FIG.  22. 

Air  Inlet  and  Exhaust  Valves  of  Hornsby-Akroyd  Oil  Motor. 
Both  valves  are  mechanically  operated. 

air  forces  part  of  it  in  through  the  narrow  neck  into  the  vaporizer 
and  mixes  it  with  the  vaporized  fuel.  The  air  is  heated  by  the 
compression  and  by  heat  received  from  the  hot  parts  of  the  motor. 
The  heat  of  the  vaporizer,  together  with  that  of  compression, 
causes  the  mixture  to  ignite  at  about  the  time  of  completion  of 


FIG.  23. 

Oil-injecting  System  of  Hornsby-Akroyd  Oil  Engine.    The  pump  discharge  is  con- 
nected to  both  the  injector  nozzle  in  the  vaporizer  and  the  regulator. 


(32) 


FIG.  24. 
Full  Side  View  of  Cylinder  End  of  Hornsby-Akroyd  Oil  Engine. 


TYPES  OF  MOTORS 


33 


the  compression  stroke.     The  inlet  and  exhaust,  ports  are  both 
closed  during  most  or  all  of  the  compression  stroke. 

Third  Stroke.  —  Impulse  stroke.  Completion  of  combustion. 
•Expansion.  Opening  of  exhaust  port.  Combustion,  accom- 
panied by  rise  of  both  temperature  and  pressure,  is  generally 
well  established  at  the  beginning  of  the  impulse  stroke.  It  is 
completed  during  the  early  part  of  the  impulse  stroke,  and  the 
increased  pressure  drives  the  piston  outward,  allowing  the  gases 
to  expand  as  the  piston  moves.  When  the  piston  has  nearly 
reached  the  end  of  the  impulse  stroke,  the  exhaust  valve  is  opened 
against  the  resistance  of  the  gas  pressure  and  a  stout  spring.  The 
contents  of  the  cylinder  partly  escape  by  expansion. 


Cock 


Gas  Reservoir. 

Flexible 

Rubber 

Diaphragm 


FIG.  25. 

Gas  Connections  for  Using  Gas  from  Small  Mains  or  through  a  Small  Connecting 
Pipe.  The  gas  reservoir  fills  between  the  suction  or  charging  strokes  of  the 
piston,  so  that  the  flexible  diaphragm  is  distended  as  shown.  The  suction  stroke 
takes  gas  from  the  reservoir,  so  that  the  diaphragm  is  drawn  in.  A  rubber  bag 
is  often  used  instead  of  the  type  of  reservoir  shown. 

Fourth  Stroke.  —  Expulsion  of  inert  gases.  The  exhaust  valve 
is  kept  open,  and  the  piston,  moving  in  toward  the  combustion 
chamber  and  vaporizer,  expels  a  portion  of  the  residual  gases. 


34  THE  GAS  ENGINE 

The  exhaust  valve  is  closed  at,  or  slightly  after,  the  end  of  the 
exhaust  stroke.  This  completes  the  series  of  events. 

In  order  that  ignition  shall  occur  at  the  proper  instant  in 
carrying  out  the  cycle  in  the  Hornsby-Akroyd  motor,  it  is  necessary 
to  have  the  intensity  of  the  compression  made  suitable  to  the 
purpose.  Too  high  compression  causes  ignition  too  long  before 
the  completion  of  the  compression  stroke,  and  too  low  com- 
pression will  not  cause  ignition  soon  enough,  or,  if  very  low,  not  at 
all.  The  usual  method  of  adjusting  the  compression  is  by  vary- 
ing the  effective  length  of  the  connecting  rod  so  as  to  cause  the 
piston  to  pass  further,  or  not  so  far,  as  the  case  may  be,  into  the 
combustion  space  end  cf  the  cylinder.  Ordinarily  this  is. done 
in  preliminary  trials  before  putting  the  motor  into  permanent 
service.  The  length  of  the  connecting  rod  is  fixed  and  a  trial 
made  to  determine  when  ignition  occurs  and  also  the  efficiency 
of  the  motor.  If  found  unsatisfactory,  the  length  of  the  con- 
necting rod  is  changed  and  fixed  at  another  length  and  another 
trial  made,  and  so  on. 

The  necessity  of  adjusting  the  length  of  the  connecting  rod 
for  each  motor  arises  from  the  fact  that,  since  the  vaporizer  and 
cylinder  are  usually  of  cast  metal,  there  is  a  variation  in  the  size 
of  those  made  from  the  same  patterns;  and  similarly,  in  large 
motors,  in  other  cast  parts,  as  the  piston  and  frame.  In  addition 
to  this  there  may  be  other  causes  necessitating  a  slight  difference 
in  the  compression  pressures  of  two  practically  similar  and  equal 
size  motors  made  from  the  same  patterns.  A  slight  difference 
in  the  form  or  composition  of  the  metal  in  the  two  vaporizers  or 
two  motors  made  from  the  same  patterns  may  make  it  necessary 
for  one  to  have  higher  compression  pressure  than  the  other  in 
order  to  produce  ignition  at  the  proper  time.  The  compression 
also  has  to  be  regulated  to  suit  the  fuel  used. 

The  compression  of  the  air  is  carried  to  about  the  same  pressure 
for  this  motor  as  is  used  in  gasoline  and  naphtha  motors  with 
electric  spark  or  arc  ignition. 

13.  Oil-Burning  Motor  with  Bulb  Ignition.  —  In  this  moW  a 
comparatively  small  hollow  bulb  of  metal  is  attached  to  the 
closed  end  of  the  cylinder,  and  the  space  in  the  bulb  is  connected 


FIG.  26. 

i 

Mietz  &  Weiss  Oil  Engine.     For  kerosene  oil  and  distillates, 
acting.     2^  to  75  horsepower  per  cylinder. 


Two-cycle,  single- 


1.  Combustion  space  of  cylinder. 

2.  Piston. 

3.  Air  port  into  crank  case. 

4.  Air  passage   from   crank   case   into 

combustion  chamber. 

5.  Inlet   port   for  air   into  combustion 

chamber. 

6.  Fuel-oil  tank. 

7.  Oil  pipe  to  plunger  pump  for  injecting 

oil  into  the  combustion  chamber. 

8.  Pump  for  forcing  oil  into  combustion 

chamber. 

9.  Pump  plunger. 

10.  Oil  pipe  to  injecting  nozzle. 

11.  Nozzle  for  injecting  fuel  oil  into  com- 


12.  Baffle  plate  opposite  oil  nozzle. 

13.  Hot  bulb  for  ignition,  cast  iron. 

14.  Exhaust  port. 

15.  Water  in  lower  part  of  jacket  for 

cooling  cylinder. 

1 6.  Steam  in  upper  part  of  jacket  space. 

17.  Steam  dome. 

1 8.  Steam  pipe  from  steam  dome  to  air 

inlet  port  5. 

19.  Oscillating  arm  for  forcing  in  the 

pump  plunger  at  each  revolution 
of  the  crank  shaft. 

20.  Coil    spring     for    forcing    pump 

plunger  outward. 

21.  Torch  for  heating  the  bulb  13  when 

starting  cold. 


bustion  chamber. 

The  amount  of  fuel  oil  forced  into  the  combustion  chamber  during  each  compres- 
sion stroke  of  the  piston  is  regulated  by  a  governor  (not  shown).  The  governor 
varies  the  movement  of  the  arm  19  toward  the  pump  plunger  9  so  as  to  give  the 
plunger  less  motion  when  the  speed  of  the  motor  increases.  The  amount  of  oil 
injected  is  thus  reduce^  as  speed  increases.  It  is  not  necessary  to  time  the 
injection  of  oil  with  any  great  accuracy. 

The  cooling  water  does  not  flow  through  and  out  of  the  jacket  space,  but  is  vapor- 
ized in  it  and  the  steam  carried  into  the  combustion  chamber  along  with  the  air. 

See  Fig.  27  for  constant-level  water  tank  that  is  attached  to  the  side  of  the  motor 
cylinder  and  connected  to  the  jacket  space. 

(35) 


THE   GAS  ENGINE 


to  the  combustion  chamber  by  a  short,  small  duct.  The  cylinder 
resembles  that  of  an  ordinary  four-stroke,  Otto-cycle  motor,  as  do 
the  other  principal  parts.  The  heat  cycle  is  nearly  the  same  as 
that  of  the  usual  types  of  gasoline  and  naphtha  motors  operating 
on  the  Otto  cycle  and  making  four  strokes  of  the  piston  per  cycle. 
The  inlet  and  exhaust  ports  open  into  the  combustion  chamber. 


-Water  to  Jacket  Space  of  Motor 
Cylinder 

(Tater  from  City  Mains  or  Overhead 
Supply  Tank 

FIG.  27. 

Constant-Level  Water  Tank  for  Mietz  &  Weiss  Horizontal  Oil  Engine.  This 
tank  is  connected  to  the  side  of  the  motor  cylinder  and  communicates  with  the 
water-jacket  space.  The  level  of  the  water  in  the  jacket  space  is  the  same  as  in 
the  tank. 

1.  Connection  to  lower  part  of  jacket  space  of  motor  cylinder. 

2.  Connection  to  upper  part  of  jacket  space  above  water  level. 

3.  Float. 

4.  Valve. 

The  bulbous  extension  attached  to  the  cylinder  head  must  be 
heated  by  an  external  flame  before  starting  the  motor.  When 
operating,  the  bulb,  generally  of  cast  iron,  is  kept  at  a  full  red 
heat.  The  liquid  fuel  is  injected  into  the  combustion  chamber 
of  the  cylinder  at  about  the  time  that  the  compression  stroke  is 
completed.  The  nozzle  from  which  the  oil  is  ejected  is  placed 
in  the  side  of  the  combustion  chamber,  and  points  so  that  the  jet 
of  oil  projected  into  the  cylinder  strikes  a  deflector  plate  extend- 
ing out  from  the  inner  end  of  the  piston,  and  part  of  it  is  deflected 
into  the  hot  bulb,  there  mixing  with  the  air  forced  into  the  latter 
during  the  compression  stroke,  vaporizing  and  igniting. 


TYPES   OF  MOTORS  37 

The  steps  of  the  operation,  starting  with  the  suction  stroke,  are: 

First  Stroke.  Suction.  —  The  outstroke  of  the  piston  draws 
in  a  cylinderful  of  air  through  the  open  inlet  valve. 

Second  Stroke.  Compression.  —  The  inlet  valve  closes  and  the 
air  is  compressed  by  the  instroke  of  the  piston.  Oil  is  injected 
just  before,  at,  or  very  slightly  after  the  completion  of  the  com- 
pression stroke.  The  oil  is  vaporized  and  ignited  by  the  heat  of 
compression  and  of  the  hot  parts  of  the  motor,  especially  the  hot 
bulb. 

Third  Stroke.  Impulse  Stroke.  —  Combustion  and  expansion 
against  the  piston  are  completed  and  the  exhaust  port  opened 
to  allow  the  inert  gases  to  escape. 

Fourth  Stroke.  —  Most  of  the  remaining  inert  gas  is  expelled 
by  the  instroke  of  the  piston. 

The  compression  of  the  air  in  this  motor  is  about  to  the  same 
intensity  as  for  gas  and  gasoline  motors  equipped  with  electric 
spark  or  arc  ignition  apparatus. 

14.  Diesel  Oil  Motor.  —  This  motor,  the  invention  of  Herr 
Rudolph  Diesel,  operates  at  a  compression  pressure  of  about 
500  pounds  per  square  inch,  which  is  vastly  higher  than  that 
used  in  any  other  internal-combustion  motor,  and  utilizes  the 
high  temperature  produced  by  compression  to  ignite  the  charge. 
It  differs  radically  from  other  motors  in  these  two  characteristics 
of  high  pressure  and  of  ignition. 

In  its  operation  a  cylinderful  of  air  is  compressed  by  the  in- 
stroke of  the  piston  into  a  very  small  space  that  corresponds  to 
the  combustion  chamber  in  an  Otto-cycle  motor.  An  oil  inlet 
valve  is  then  opened  and  oil  is  blown  in  by  compressed  air  taken 
from  tanks  separate  from  the  motor.  The  air  pressure  of  the 
tanks  is,  of  course,  higher  than  that  in  the  combustion  cylinder. 
The  first  particles  of  oil  are  ignited  and  burned  as  soon  as  they 
enter  the  hot  compressed  air  in  the  combustion  cylinder,  and  so 
on  with  all  the  oil  that  follows.  The  burning  is  somewhat 
gradual,  as  compared  with  the  explosion  in  other  motors,  since 
the  oil  is  blown  in  slowly  in  comparison  with  the  speed  of  the 
piston.  The  pressure  is  therefore  not  increased  much,  if  any, 
above  that  of  compression,  but  is  kept  up  as  the  piston  recedes, 


38  THE  GAS  ENGINE 

by  the  constant  influx  of  fuel,  until  the  oil  inlet  valve  closes.  The 
hot  gases  in  the  cylinder  then  continue  to  expand  and  drive  out 
the  piston  until  the  exhaust  port  is  opened.  The  cylinder  is 
partly  cleared  of  inert  gases  during  the  next  stroke  of  the  piston, 
and  fresh  air  is  drawn  in  by  suction  during  the  following  stroke. 
Crude  petroleum  can  be  used  for  fuel. 

The  fuel  is  blown  in  through  an  atomizer  of  unusual  construc- 
tion which  is  made  up  of  broad  rings  resembling  washers,  with 
grooved  faces  and  small  perforations.  The  rings  are  placed  side 
by  side  on  the  oil-valve  stem  in  sufficient  number  to  form  a  column 
several  times  as  long  as  their  diameter.  The  compressed  air 
from  the  auxiliary  tanks  passes  through  the  nest  of  disks  and 
becomes  thoroughly  impregnated  with  the  oil,  thus  securing  the 
best  mechanical  condition  for  rapid  combustion. 

On  account  of  the  extremely  high  compression  pressure  and 
the  comparatively  large  size  of  the  Diesel  motors  that  have  been 
put  into  operation,  they  cannot  be  conveniently  started  by  hand 
power.  Compressed  air  from  a  storage  tank  is  used  for  starting. 
The  motor  is  barred  over  by  hand  till  the  piston  is  just  beginning 
the  outstroke  with  the  valves  closed  as  for  the  impulse  stroke. 
A  hand  valve  from  the  compressed-air  starting  tank  is  then 
opened  and  the  high  pressure  enters  the  cylinder  and  drives  the 
piston  outward.  The  motor  starts  quickly  under  the  high 
pressure  and  the  hand  valve  must  be  promptly  closed. 

The  auxiliary  air  tanks  are  filled  by  a  separately  driven  air 
compressor.  These  tanks  are  charged  by  means  of  power  from 
the  motor  while  it  is  running. 

The  speed  of  the  motor  is  controlled  by  the  action  of  a  centrif- 
ugal governor  that  regulates  the  quantity  of  oil  fuel  forced  into 
the  nest  of  atomizing  washers  or  disks,  from  which  it  is  carried 
into  the  cylinder  by  the  compressed  air.  The  regulating  devices 
that  are  used  operate  in  various  ways,  generally  on  a  pump,  each 
stroke  of  which  forces  a  charge  of  oil  into  the  cylinder  by  varying 
the  length  of  stroke  of  the  pump,  the  extent  of  the  opening  of  an 
oil  by-pass  valve,  etc.  The  fuel  valve  closes  early  in  the  stroke, 
and  the  pressure  in  the  combustion  cylinder  drops -well  toward 
atmospheric  by  the  time  the  exhaust  valve  opens. 


TYPES   OF  MOTORS  39 

On  account  of  the  high  compression  and  great  expansion,  the 
combustion  cylinder  (combustion  chamber  and  cylinder  together) 
and  the  stroke  of  the  piston  are  longer,  in  comparison  with  their 
diameters,  than  is  customary  in  other  internal-combustion  motors 
and  in  steam  engines.  This  is  on  account  of  constructive  prin- 
ciples, and  is  not  otherwise  necessary  to  secure  the  high  com- 
pression and  great  expansion. 

Pioneer  Internal-Combustion  Motors. 

15.  The  earliest  gas  engine  commercially  used  (still  shown  as 
a  historical  exhibit)  has  a  vertical  cylinder  open  at  the  top  and 
with  the  inlet  and  exhaust  ports  at  the  bottom.  The  piston  is 
connected  to  a  horizontal  shaft  placed  above  the  cylinder  and 
carrying  a  flywheel.  The  connection  between  the  piston  and 
shaft  is  by  means  of  a  spur  gear  wheel  on  the  shaft  and  a  toothed 
rack  on  the  piston,  instead  of  the  now  customary  smooth  piston 
rod.  The  gear  is  connected  to  the  shaft  by  a  pawl  and  ratchet, 
so  that  it  is  free  to  turn  around  the  shaft  in  one  direction  but 
not  in  the  other.  The  piston  is  therefore  free  to  move  upward 
when  a  charge  is  exploded  under  it,  but  when  descending  it 
drives  the  shaft  by  means  of  the  gear  wheel  and  ratchet.  The 
descent  of  the  piston  is  due  to  its  own  weight  only,  unless  the 
speed  is  very  slow.  Then  the  cooling  and  contraction  of  the  gas 
after  combustion  may  produce  a  partial  vacuum. 

In  the  operation  of  this  free-piston  motor  the  piston  is  lifted 
through  part  of  its  stroke  from  its  lowest  position  by  means  of  a 
connection,  for  this  purpose,  with  the  rotating  flywheel  shaft. 
The  combustible  charge  is  drawn  in  by  suction  during  this  early 
part  of  the  piston's  upward  motion.  When  the  piston  has  reached 
a  certain  height  the  charge  is  ignited  at  about  atmospheric 
pressure,  and  the  explosion  projects  the  piston  farther  upward 
at  a  higher  velocity  than  it  had  been  traveling.  It  moves  upward 
freely  until  stopped  by  gravity  and  friction,  then  descends  by 
gravity  and  drags  the  flywheel  shaft  around,  at  the  same  time 
expelling  the  inert  products  of  combustion  through  the  exhaust 
port,  which  opens  when  the  piston  begins  to  descend.  This 


40  THE   GAS  ENGINE 

is  the  cycle  that  is  repeatedly  performed  while  the  motor  is 
running. 

Motors  operating  on  the  same  cycle  (heat  cycle  of  the  gases) 
as  the  free-piston  motor  just  described,  but  having  a  cranked 
flywheel  shaft  and  a  fixed-length  connecting  rod  between  the 
piston  and  crank  shaft,  were  constructed  soon  after  the  free- 
piston  motor. 

In  comparison  with  motors  in  which  the  combustible  charge 
is  compressed  before  ignition,  and  which  were  brought  out  after 
the  ones  just  mentioned,  the  free-piston  motor  and  all  other 
internal-combustion  motors  in  which  the  charge  is  not  com- 
pressed before  ignition,  are  inefficient  in  transforming  the  heat  of 
combustion  into  mechanical  energy.  They  are  uneconomical  of 
fuel  and  heavy  in  weight  in  proportion  to  their  power  capacity. 
When  motors  operating  on  the  Beau  de  Rochas  or  Otto  cycle 
appeared,  the  earlier  non-compressing  types  were  discarded  from 
commercial  power  generation  use. 

Scavenging. 

1 6.  In  four-cycle  motors  following  the  Otto  cycle  approximately 
there  is  a  considerable  volume  of  the  gaseous  products  of  combus- 
tion left  in  the  motor  cylinder  after  the  exhaust  stroke  of  the 
piston  is  completed,  unless  some  special  provision  is  made  for 
removing  them.  These  inert  residual  gases  mingle  with  the 
next  charge  that  enters  and  dilute  it.  While  this  dilution  affects 
the  economy  of  the  motor  but  little,  if  any,  it  reduces  the  power 
capacity  by  preventing  a  complete  cylinderful  of  the  combustible 
mixture  from  entering. 

Some  experiments  were  made  in  England  on  a  small  four- 
cycle motor  to  find  what  increase  of  power  could  be  secured  by 
removing  the  residual  gaseous  products  of  combustion  before 
taking  in  a  fresh  charge.  The  method  of  scavenging  the  cylinder 
with  pure  air  was  very  simple.  A  long,  straight  exhaust  pipe  was 
connected  to  the  motor.  The  length  of  the  exhaust  pipe  was  so 
proportioned  by  experimentation  that  the  inertia  of  the  gases 
passing  out  rapidly  when  the  exhaust  valve  opened,  induced  a 


TYPES  OF  MOTORS  41 

partial  vacuum  at  the  motor  end  of  the  pipe  at  fche  instant  of 
opening  the  inlet  valve.  When  the  inlet  opened,  the  suction  due 
to  the  inertia  of  the  escaping  portion  of  the  exhaust  gases  drew 
the  remaining  portion  out  of  the  cylinder  and  fresh  air  into  it. 
The  fuel-gas  valve  was  not  opened  till  some  air  had  passed  into 
the  motor  cylinder.  Some  gain  in  the  power  capacity  of  the 
motor  was  thus  secured. 

The  Atkinson  four-cycle  motor,  already  mentioned,  can  be 
classed  as  a  scavenging  motor,  since  its  piston  goes  so  far  into  the 
compression  space  on  the  exhaust  stroke  as  to  drive  out  nearly 
all  of  the  inert  gases. 

Two-cycle  motors  that  have  air  and  gas  compressors  are 
scavenging  motors  when  enough  air  is  let  in  to  drive  out  nearly 
all  the  products  of  combustion  before  the  combustible  mixture 
of  air  and  gas  is  passed  into  the  cylinder.  The  more  simple  form 
of  two-cycle  motor  that  precompresses  the  combustible  mixture 
in  the  crank  case  can  hardly  be  classed  as  a  scavenging  motor. 

The  advantages  of  scavenging  in  the  four-cycle  motor  have  not 
yet  appeared  great  enough  to  warrant  the  more  complicated 
construction  necessary  to  secure  it. 

Compound  Motors. 

17.  Motors  in  which  the  expansion  of  the  gaseous  products  of 
combustion  is  carried  out  to  a  greater  degree  by  the  aid  of  a 
secondary  low-pressure  cylinder  than  in  the  usual  types  where 
all  the  expansion  is  in  the  combustion  cylinder,  are  constructed 
to  a  small  extent. 

One  of  the  most  recent  four-cycle  compound  motors,  used  for 
driving  an  automobile,  has  two  vertical  combustion  cylinders  of 
the  same  size,  with  a  secondary  low-pressure  expansion  cylinder 
between  them.  The  pistons  and  all  the  cylinders  are  single- 
acting.  The  length  of  stroke  of  all  three  pistons  is  the  same,  but 
the  low-pressure  cylinder  is  of  greater  diameter  than  the  others. 
The  two  high-pressure  pistons  (those  in  the  combustion  cylinders) 
move  up  and  down  in  unison,  while  the  low-pressure  piston 
moves  in  the  opposite  direction.  The  crank  angle  between  the 


42  THE   GAS  ENGINE 

low-pressure  crank  and  the  high-pressure  cranks  is  180  degrees 
or  half  a  revolution.  There  is  no  angle  between  the  two  high- 
pressure  cranks. 

The  high-pressure  cylinders  are  each  provided  with  an  inlet 
and  an  outlet  port,  both  opening  into  the  combustion  chamber  in 
the  usual  manner. 


FIG.  28. 

Compound  Motor.    Four-Cycle,  Three-Cylinder  Automobile  Type.     12  to  15  horse- 
power.   Section  on  plane  of  cylinder  axes, 
i  and  2  are  the  combustion  or  high-pressure  cylinders. 
3  is  the  intermediate  low-pressure  cylinder. 

The  upper  end  of  the  low-pressure  cylinder  is  connected  to  each  of  the  high-pressure 
cylinders  by  short  passages  with  valves.  The  exhaust  from  the  high-pressure 
cylinders  passes  into  the  low-pressure  cylinder,  so  that  its  piston  is  given  an 
impulse  every  downstroke. 

The  method  of  operating  is  as  follows,  dealing  with  the  forward 
cylinder  first  for  convenience:  The  exhaust  gases  from  the 
forward  high-pressure  cylinder  follow  a  short  passage  into  the 
low-pressure  cylinder  and  through  one  of  the  inlet  valves  of  the 
latter.  The  exhaust  valve  of  the  forward  high-pressure  cylinder 
and  the  corresponding  inlet  valve  of  the  low-pressure  cylinder  are 
opened  and  closed  in  unison.  They  open  about  the  time  of 
completion  of  the  explosion  stroke,  and  remain  open  about  half 


TYPES  OF  MOTORS  43 

a  revolution  of  the  crank,  while  the  upstroke  of  tl\e  high-pressure 
piston  in  a  vertical  engine  forces  the  chemically  inert  gases  into 
the  low-pressure  cylinder,  whose  cylinder  is  descending  on  its 
impulse  stroke.  During  this  part  of  the  operation  the  pressure 
of  the  gases  on  the  two  pistons  is  about  the  same  per  square  inch 
for  both,  but  is  slightly  lower  in  the  low-pressure  cylinder.  Since 
the  piston  area  of  the  latter  is  greater  than  for  the  high-pressure 
cylinder,  the  low-pressure  piston  delivers  a  turning  moment  to 
the  crank  which  is  greater  than  the  resisting  moment  of  the  high- 
pressure  piston.  The  net  result  is  that  the  additional  expansion 
of  the  gases  develops  mechanical  power. 

At  about  the  completion  of  the  downstroke  of  the  low-pressure 
piston  its  inlet  valve  closes  (together  with  the  exhaust  valve  of 
the  forward  high-pressure  cylinder)  and  its  exhaust  valve,  at  the 
upper  end  of  the  cylinder,  is  opened  to  allow  the  escape  of  the 
thoroughly  expanded  gases  into  the  atmosphere  as  the  low- 
pressure  piston  moves  upward.  A  similar  operation  is  then 
carried  out  by  the  rear  combustion  cylinder  and  the  low-pressure 
cylinder.  The  latter  has  two  inlet  valves,  one  for  each  of  the 
high-pressure  cylinders. 

The  crank  shaft  receives  an  impulse  at  every  half  revolution 
to  keep  up  its  rotation.  The  impulses  on  the  crank  shaft  come 
in  the  following  order:  forward  piston,  low-pressure  piston,  rear 
piston,  low-pressure  piston. 

An  earlier  type  of  compound  motor,  an  English  production, 
has  one  high-pressure  and  one  low-pressure  cylinder.  They  are 
placed  side  by  side  close  together,  and  the  combustion  chamber 
of  the  high-pressure  one  is  connected  by  a  large  open  passage  to 
the  closed  end  of  the  other.  The  low-pressure  cylinder  has,  of 
course,  the  greater  volume.  The  pistons  are  connected  to 
separate  crank  shafts,  which  are  parallel  to  each  other  and  geared 
together  so  that  the  one  for  the  high-pressure  cylinder  makes 
two  revolutions  to  one  of  that  for  the  low-pressure  cylinder. 
The  crank  shafts  are  geared  together  in  such  a  manner  that  the 
high-pressure  piston  makes  nearly  a  complete  stroke,  imme- 
diately following  combustion,  by  the  time  the  low-pressure  piston 
has  moved  a  very  small  portion  of  its  outstroke.  Both  pistons  are 


44  THE   GAS  ENGINE 

single  acting.  The  low-pressure  piston  then  moves  out  rapidly 
while  the  high-pressure  one  is  completing  the  small  remaining 
part  of  its  outstroke  and  moving  back  a  short  distance  on  its 
exhaust  stroke,  and  so  on. 

A  double-acting,  four-cycle,  compound  motor  of  this  type  with 
two  high-pressure  and  two  low-pressure  cylinders  was  recently 
constructed  in  this  country  with  a  view  to  using  it  for  boat  pro- 
pulsion. There  were  some  modifications,  however,  in  the  design 
which,  while  not  changing  the  appearance  of  the  motor,  had 
a  great  effect  on  its  operation.  The  most  notable  change  was 
the  placing  of  a  large  automatic  valve  in  the  passage  between  the 
high-pressure  and  low-pressure  cylinders  so  that  none  of  the 
gases  could  pass  from  the  latter  to  the  former.  There  may  have 
been  certain  advantages  to  be  gained  by  doing  this.  But,  in 
addition  to  this,  an  igniting  device  was  placed  in  the  low-pressure 
cylinder  as  well  as  in  the  combustion  cylinder.  The  result  was 
as  might  well  be  expected.  When  the  motor  was  started  some 
of  the  combustible  mixture  entered  the  low-pressure  cylinder  on 
account  of  a  missed  explosion  or  some  other  cause.  The  igniter 
fired  it  in  the  low-pressure  cylinder  and  the  explosion  closed  the 
intermediate  valve  with  such  force  as  to  shatter  it.  The  same 
injury  might  have  occurred  without  the  ignition  device  in  the 
low-pressure  cylinder,  after  a  misfire  in  the  high-pressure  one. 

Impulse  Frequency  for  Different  Arrangements  of  Cylinders. 

1 8.  The  following  are  the  more  customary  methods  of  arrang- 
ing the  cylinders  of  motors,  and  the  corresponding  number  of 
impulses  delivered  to  the  crank  shaft: 

Two  revolutions  of  crank  shaft  for  each  impulse: 
Four-cycle,  single-acting,  single-cylinder  motor. 
Four-cycle,  single-cylinder  motor  with  combustion  chamber  at 
middle  of  cylinder  and  two  opposed  pistons  that  recede 
from  the  middle  of  the  cylinder  at  the  same  time  toward  the 
open  ends  of  the  cylinder  during  the  impulse  stroke,  and 
then  return  at  the  same  time  during  the  compression  stroke. 


TYPES   OF    MOTORS  45 

One  revolution  for  each  impulse: 

Two-cycle,  single-acting,  single-cylinder  motor. 

Four-cycle,  single-acting,  two-cylinder  motor  with  opposed 
cylinders  on  opposite  sides  of  the  crank  shaft  and  cranks  at 
1 80  degrees. 

Four-cycle,  single-acting,  two-cylinder  motor  with  the  cylinders 
on  the  same    side  of    the    crank  shaft  and  the  cranks  at 
o  degrees.     (Twin  cylinders  in  some  designs.) 
Two-thirds  of  a  revolution  for  each  impulse: 

Four-cycle,  single-acting,  three-cylinder  motor  with  all  three 
cylinders  on  the  same  side  of  the  crank  shaft  and  the  cranks 
at  120  degrees. 
One-half  revolution  for  each  impulse: 

Two-cycle,  single-acting,  two-cylinder  motor  with  both  cylin- 
ders on  the  same  side  of  the  crank  shaft  and  the  cranks  at 
1 80  degrees.  (Twin  cylinders  in  some  designs.) 

Compound  motor,  four-cycle,  single-acting,  three  cylinders. 
Two  high-pressure  or  combustion  cylinders  and  one  low- 
pressure  or  expansion  cylinder,  all  three  on  same  side  of 
the  crank  shaft.  Low-pressure  crank  at  180  degrees  with 
the  pair  of  high-pressure  cranks.  High-pressure  pistons 
move  in  unison  in  one  direction,  while  the  low-pressure  piston 
moves  in  the  opposite  direction. 

Four-cycle,  single-acting,  four-cylinder  motor  with  all  cylinders 
on  the  same  side  of  the  crank  shaft  and  one  pair  of  crank 
shafts  at  180  degrees  with  the  other  pair.  One  pair  of 
pistons  move  in  unison  in  one  direction,  while  the  other  pair 
move  in  the  opposite  direction. 

Four-cycle,  double-acting  pair  of  tandem  cylinders  with  one 

crank. 
One-third  revolution  for  each  impulse: 

Two-cycle,  single-acting,  three-cylinder  motor  with  all  three 
cylinders  on  the  same  side  of  the  crank  shaft  and  the  three 
cranks  at  120  degrees. 

Four-cycle,  single-acting,  six-cylinder  motor  with  all  six  cylin- 
ders on  the  same  side  of  the  crank  shaft  and  the  cranks  at 
120  degrees  in  pairs. 


46  THE   GAS  ENGINE 

Reversing  the  Rotation  of  the  Motor. 

19.  The  direction  of  rotation  that  the  first  impulse  gives  the 
motor  shaft  depends  only  on  the  position  of  the  crank  at  the 
instant  of  ignition.  This  assumes  that  the  motor  is  rotating  at 
only  a  very  slow  speed,  or  not  at  all.  The  four-cycle  motor, 
unless  provided  with  mechanism  for  changing  the  time  of  valve 
action,  will  soon  stop  if  the  first  impulse  starts  it  in  the  wrong 
direction.  Such  reversing  mechanism  has  not  come  into  use  for 
four-cycle  motors. 

The  two-cycle  motor  will  continue  to  rotate  in  the  direction 
that  the  first  impulse  gives  it  when  of  the  simple  type  that  com- 
presses its  charge  in  the  crank  case,  if  the  timer  is  adjusted  so  as 
to  continue  to  give  ignition  at  the  proper  time.  The  absence  of 
mechanically  operated  valves,  or  of  all  valves,  makes  this  possible. 

The  method  of  reversing  small  two-cycle  motors  of  this  class, 
such  as  launch  motors,  is  to  cut  out  the  ignition  and  allow  the 
motor  to  slow  down.  The  timer  is  then  set  to  give  ignition  before 
dead  center  is  reached,  as  the  motor  is  still  rotating,  provided  the 
timer  is  not  already  in  this  position.  The  igniter  is  put  into 
action  again  when  the  motor  has  nearly  stopped,  and  the  first 
impulse  reverses  the  motor.  The  timer  is  then  adjusted  to  the 
proper  setting  for  the  reversed  rotation.  The  motor  may  be 
throttled  during  the  reversing  to  prevent  too  strong  an  impulse 
at  the  instant  of  reversal. 


CHAPTER  II. 

CARBURATION,  CARBURETERS,  PREHEATING  THE  CHARGE, 
FUEL  SUPPLY. 

C arbitration  of  Air. 

20.  A   motor  that   receives   into   its   combustion   cylinder  a 
charge  composed  of  a  mixture  of  air  and  vapor  of  some  volatile 
hydrocarbon  which  is  normally  a  liquid  at  atmospheric  temper- 
ature and  pressure,  must  be  provided  with  some  kind  of  a  car- 
bureter for  enriching  the  air  with  fuel  on  its  way  to  the  cylinder. 

The  spray  carbureter  has  come  into  general  use  for  naphtha 
and  gasoline  in  this  country.  The  characteristic  of  this  type  is 
that  the  liquid  hydrocarbon  is  drawn  out  of  a  small  nozzle,  or 
group  of  nozzles,  by  the  suction  of  the  air  going  to  the  com- 
bustion cylinder,  or,  in  the  two-cycle  motors,  by  the  air  going 
into  the  crank  case  of  the  primary  compression  cylinder.  The 
suction  that  causes  the  flow  of  liquid  fuel  is  aided  by  gravity  in 
some  types  of  the  spray  carbureter. 

One  carbureter  will  supply  either  one  or  more  combustion 
chambers  or  cylinders.  It  is  general  practice  to  use  only  one 
carbureter  for  a  multi-cylinder  motor. 

21.  Primer    for    Carbureter   using   Volatile    Fuel.  —  It    fre- 
quently happens  that  a  carbureter  will  not  sufficiently  enrich 
the  air  in  the  usual  manner  when  starting  the  motor.     In  order 
to  prime  the  carbureter,  many  are  therefore  provided  with  a 
means  of  causing  more  fuel  than  usual  to  flow  from  the  spray 
nozzle  just  before  starting  the  motor.     The  device  for  doing  this 
is  called  a  primer.     It  is  a  simple  hand-operated  arrangement 
that  depresses  the  float  of  a  float-feed  carbureter,  or  opens  the 
fuel  valve  otherwise  in  other  types,  so  that  some  of  the  liquid 
can  flow  out  into  the  mixing  chamber  or  air  passage  without 
the  aid  of  the  suction  of  the  motor. 

47 


Gasoline  level 
when  engine  is|||||| 
at  rest 


FIG.  29. 
Spray  Nozzle  Carbureter.     Sectional  View. 

The  gasoline  is  supplied  from  some  source  that  maintains  a  level  somewhat  lower 
than  the  open  upper  end  (nozzle)  of  the  vertical  gasoline  pipe.  The  air  current 
passes  up  by  the  nozzle  during  the  charging  stroke  of  the  motor.  The  partial 
vacuum  due  to  the  suction  of  the  motor  draws  gasoline  from  the  nozzle.  The 
gasoline  immediately  vaporizes  and  mixes  with  the  air.  The  amount  of  gasoline 
drawn  out  is  regulated  by  the  small  valve  at  the  elbow  of  the  supply  pipe.  It 
can  also  be  regulated  by  the  butterfly  valve  in  the  horizontal  part  of  the  air  pipe. 
When  this  air  valve  is  turned  from  the  horizontal  position  shown,  so  as  to  par- 
tially close  the  air  inlet,  a  greater  degree  of  vacuum  is  formed  at  the  spray  nozzle 
and  more  gasoline  drawn  out,  thus,  making  a  richer  mixture.  The  real  use  of  the 
air  valve,  however,  is  generally  for  causing  enough  gasoline  to  be  drawn  out  when 
starting  the  motor.  The  slow  speed  at  starting,  as  by  hand  cranking,  does  not 
produce  suction  enough  to  draw  out  sufficient  gasoline  when  the  air  valve  is  open 
as  shown.  But  closing  it  will  cause  enough  fuel  to  be  drawn  out  to  make  a 
mixture  rich  enough  for  igniting.  In  such  cases  the  air  valve  is  opened  com- 
pletely after  starting. 

(48) 


CARBURATION 


49 


14 


12 


Float-Feed  Spray  Carbureter.     Wheeler  &  Schebler,  Indianapolis,  Ind. 

The  gasoline  flows  up  past  the  valve  i  into  the  reservoir  (float  chamber)  2.  As 
the  gasoline  rises  in  the  reservoir  it  lifts  the  cork  float  3  (which  is  horseshoe 
shaped  and  extends  around  the  sides  of  the  main  air  passage).  The  float  is 
fastened  to  an  arm  that  is  pivoted  at  4  and  engages  with  the  upper  end  of  the 
stem  of  valve  i.  When  the  float  rises  to  the  proper  height  it  closes  the  valve  i 
and  stops  the  inflow  of  gasoline  at  a  level  slightly  lower  than  that  of  the  spray 
nozzle  5.  The  needle  valve  6  is  for  regulating  the  size  of  the  passage  to  the  spray 
nozzle. 

When  starting  the  motor  the  air  all  enters  through  the  bottom  air  passage  7  whose 
orifice  into  the  main  air  passage  surrounds  the  spray  nozzle.  The  passage  7  is 
always  left  full  open.  The  mixture  passes  out  as  indicated.  When  the  motor 
is  running,  air  also  enters  at  the  upper  inlet  passage  8  by  opening  the  valve  9 
against  the  resistance  of  the  coil  spring  10.  The  gate  valve  n,  shown  partly 
closed,  acts  as  a  throttle  to  the  passage  of  the  mixture  from  the  carbureter.  It  is 
operated  by  the  lever  (or  bell  crank)  12.  The  throttle  can  be  prevented  from 
completely  closing  by  the  adjustable  screw  13  against  which  a  projection  on  the 
lever  13  strikes. 

The  force  exerted  by  the  spring  10  for  holding  the  compensating  air  valve  9  closed 
is  regulated  by  the  wing  nut  14. 

For  priming  or  flushing  the  carbureter,  the  vertical  pin  15  is  pressed  down  against 
the  cork  float.  This  can  be  done  by  pulling  a  wire  or  string  attached  to  the 
bell  crank  16. 


50  THE   GAS  ENGINE 

Another  method  of  priming  the  motor  is  to  put  the  volatile 
fuel  directly  into  the  combustion  chamber.  A  pet-cock  (often 
with  a  cup-shaped  end  to  be  used  as  a  measure)  is  generally 
provided  for  this  purpose. 

22.  Float-Feed  Spray  Carbureter  for  Volatile  Liquids.  —  The 
float-feed  spray  carbureter  has  a  small  reservoir  in  which  a 
hollow  metal  or  a  cork  float  is  buoyed  up  by  the  liquid  fuel. 
The  float  is  connected  to  a  cone-point  valve  (float  valve)  which, 
when  the  float  is  lifted  to  a  certain  height,  stops  the  opening 
through  which  the  liquid  enters  from  the  main  tank  in  which 
the  bulk  of  the  fuel  is  carried.  The  short  duct  that  terminates 
as  the  orifice  of  the  nozzle  is  led  from  the  carbureter  reservoir 
into  the  air  passage  through  which  air  is  drawn  into  the  motor. 
This  duct  starts  some  distance  below  the  level  of  the  liquid,  and 
the  nozzle  terminates  a  slight  distance  above  the  level  of  the 
liquid  maintained  by  the  float.  The  latter  is  adjusted  to  main- 
tain this  level  at  about  one-sixteenth  to  one-eighth  of  an  inch 
below  the  nozzle  in  most  cases,  but  the  nozzle  is  sometimes  as 
much  as  an  inch  higher  than  the  level  of  the  fuel. 

As  the  air  is  drawn  through  the  air  passage,  its  suction  draws 
the  liquid  from  the  nozzle  and  it  is  vaporized  almost  instantly 
when  the  conditions  are  favorable.  Drawing  the  liquid  from  the 
nozzle  lowers  its  level  in  the  small  reservoir  of  the  carbureter, 
and  the  float  falls  so  as  to  open  the  float  valve  for  letting  in  more 
liquid  and  maintaining  the  proper  level. 

The  rate  of  flow  of  fuel  from  the  nozzle  in  proportion  to  the 
rate  of  flow  of  air  past  it  is  adjusted  by  a  needle  valve  that 
partially  stops  the  nozzle  orifice  or  the  passage  leading  to  it. 
This  is  the  only  adjustment  in  several  makes  of  float-feed  car- 
bureters. Others,  however,  that  are  increasing  in  proportion 
of  numbers  used  have  an  air  valve  that  is  used  to  regulate  the 
intensity  of  suction  at  the  fuel  nozzle.  In  many  modern  designs 
a  single  air  valve  is  placed  so  that  the  air  passes  through 
it  before  reaching  the  nozzle;  the  air  valve  is  held  to  its  seat  by 
a  weak  spring  except  when  lifted  by  suction.  By  adjusting 
both  the  needle  valve  and  the  air  valve  the  mixture  "can  be  given 
correct  proportions,  within  practical  limits,  for  very  greatly 


CARBURATION  5 1 

different  rates  of  flow  of  the  air.  In  other  words,.the  carbureter 
can  be  adjusted  to  keep  the  mixture  ratio  of  air  and  fuel  prac- 
tically constant  for  a  motor  that  runs  at  greatly  different  speeds 
and  whose  power  and  speed  are  controlled  by  throttling  the 
charge  at  a  point  between  the  carbureter  and  the  motor.  It  is 
not  unusual  to  find  the  spring-closed  air  valve  in  other  parts  of 
the  carbureter. 

In  some  types  of  carbureters  in  which  no  spring-seated  air 
valve  is  used,  two  valves  of  the  wing  type  that  is  common  in 
stovepipes,  etc.,  are  used.  One  is  placed  between  the  fuel  nozzle 
and  the  motor,  and  the  other  between  the  nozzle  and  the  air 
intake  of  the  carbureter.  They  are  then  both  moved  in  con- 
junction to  control  the  speed  and  power  of  the  motor.  By  this 
means  both  the  speed  of  flow  of  the  air  and  the  intensity  of 
suction  at  the  fuel  nozzle  are  simultaneously  regulated. 

An  adjustable  stop  to  limit  the  lift  of  the  air  valve  is  provided 
in  some  designs,  but  this  is  unusual. 

In  carbureters  for  automobile  motors  the  small  liquid  reservoir 
generally  surrounds  the  air  passage  and  the  nozzle  more  or  less 
completely.  The  chief  reason  for  this  form  of  construction  is  to 
provide  a  means  to  keep  the  level  of  the  fuel  in  the  nozzle  constant 
when  the  carbureter  is  tipped  by  the  car  passing  over  hilly  and 
uneven  roads.  The  earlier  types,  and  some  still  on  the  market, 
were  made  with  the  small  reservoir  at  one  side  of  the  air  passage 
and  nozzle;  this  results,  in  some  cases,  in  a  lack  of  uniform 
carburation  of  the  air  when  passing  over  uneven  roads. 

A  throttle  valve  is  often  placed  in  the  carbureter  between  the 
fuel  nozzle  and  the  motor.  Wing  and  shutter  type  throttle 
valves  are  in  common  use,  as  are  tubular  forms. 

While  only  one  fuel  nozzle  is  the  rule  in  float-feed  carbureters, 
some  are  made  with  several  nozzles  of  the  same  size  that  act 
simultaneously.  In  more  unusual  designs,  nozzles  of  different 
sizes  are  provided,  all  placed  at  the  same  level.  This  type  of 
carbureter  is  intended  for  motor  cars  where  the  demand  for 
mixture  varies  between  wide  limits.  A  large  nozzle  delivers 
the  liquid  fuel  when  the  demand  for  power  is  great,  as  when 
climbing  a  hill,  but  when  the  throttle  control  is  readjusted  for 


52  THE  GAS  ENGINE 

light  power  on  a  good,  level  road,  the  large  nozzle  is  cut  out  and 
a  small  one  brought  into  action. 

23.  Pump-Feed  Spray  Carbureters  for  Volatile  Fuel.  —  For 
stationary  and  other  motors  where  the  supply  of  fuel  is  carried 
below  the  level  of  the  carbureter,  and  no  air  pressure  is  used  to 
raise  the  liquid  to  the  level  of  the  carbureter,  the  open  spray 
nozzle  type,  in  which  the  constant  level  of  the  fluid  fuel  in  the 
small  reservoir  of  the  carbureter  is  maintained  by  a  pump,  finds 
considerable  use^     The  fuel  pump  generally  forms  part  of  the 
motor  and  is  naturally  very  small.      It  pumps  more  fuel  than 
the  motor  requires  at  any  time,  and  the  level  is  maintained  by  an 
overflow  pipe  or  opening  that  takes  the  surplus  fuel  back  to  the 
main  supply  tank  or  its  connections. 

24.  Pump-Feed   Carbureter  with   Measuring   Cup.  —  In   this 
type  a  small  pump  lifts  the  liquid  fuel  from  the  main  tank  and 
discharges  it  into  a  small  measuring  cup  or  pipe  end  in  the  air 
inlet  pipe  of  the  motor.     The  capacity  of  the  measuring  cup  is 
that  for  the  amount  of  fuel  required  for  one  full  charge  of  the 
motor.     The  pump  supplies  more  fuel  than  sufficient  to  fill  the 
cup,  and  the  overflow  returns  to  the  main  reservoir.     The  cup 
is  filled  by  the  pump  during  the  strokes  of  the  motor  piston  that 
come  between  impulse  strokes.     The  suction  of  the  air  on  its 
way  to  the  motor  combustion  cylinder  empties  the  cap  of  its 
complete  charge  of  fuel.     This  type  of  carbureter  is  not  suitable 
for  use  in  connection  with  a  throttle  in  the  air  passage. 

25.  Disk-Feed  Spray   Carbureter  for  Volatile   Liquids.  —  In 
this  type  of  carbureter  the  vertical  fuel  nozzle  opens  upward 
and  is  closed  by  a  cone-point  valve  that  points  downward  and 
rests  in  the  orifice  by  gravity  and  prevents  the  flow  of  liquid 
when  none  is  needed.     The  valve  spindle  is  vertical  and  has  a 
thin  metal  disk  attached  to  it.     The  disk  is  placed  in  and  partly 
closes  the  air  passage  leading  to  the  motor  combustion  cylinder. 
When  a  charge  is  drawn  into  the  motor,  the  air,  flowing  upward 
past  the  nozzle  and  disk,  lifts  the  latter  and  the  valve  attached 
to  it,  and  thus  opens  the  orifice  so  that  the  liquid  fuel  can  flow 
out  into  the  passage  for  air,  where  it  is  vaporized  and  carried  by 
the  air  to  the  motor. 


CARBURATION  53 

The  supply  tank  is  placed  higher  than  the  nozzle,  and  the 
flow  of  the  liquid  is  caused  by  both  gravity  and  suction,  except 
when  a  compression  supply  tank  is  used,  in  which  case  the 
compression  pressure  lifts  the  liquid  to  the  nozzle. 

In  order  to  keep  the  valve  and  its  seat  free  from  dirt  or  deposit, 
the  disk  has  a  few  tongue-shaped  pieces  cut  out  of  it  except  at 
the  part  corresponding  to  the  base  of  the  tongue,  and  the  point 
of  each  tongue  bent  up  slightly  to  make  an  opening  through 
which  the  air  can.  pass.  This  tongue  somewhat  resembles  the 
reed  of  a  musical  instrument.  The  length  of  each  tongue  is 
parallel  to  the  periphery  of  the  disk,  and  all  are  pointed  in  the 
same  direction  with  regard  to  the  rotation  of  the  disk  about  the 
valve  stem.  As  the  air  passes  through  the  openings  and  strikes 
the  tongues  it  causes  the  disk  and  valve  stem  to  rotate  some- 
what in  the  manner  of  a  wind  motor,  so  that  the  valve  spins 
slightly  on  its  seat  when  it  settles  down. 

The  adjustment  for  securing  the  proper  proportions  of  air  and 
fuel  in  the  mixture  is  made  by  regulating  the  height  of  the  lift 
of  the  valve.  This  is  ordinarily  done  by  means  of  an  adjusting 
screw  that  is  placed  above  the  valve  and  disk  and  is  concentric 
with  the  valve  stem. 

A  spring-closed  and  adjustable  air  valve  can  be  used  in  this 
carbureter  as  well  as  in  other  types.  The  same  is  true  of  throttle 
valves.  They  are,  in  fact,  both  used. 

26.  Diaphragm-Feed  Spray  Carbureters  for  Volatile  Liquids. 
—  In  this  type  the  vertical  fuel  nozzle  is  closed  by  a  cone-point 
valve  whose  stem  is  generally  vertical.  A  circular  diaphragm  is 
attached  to  the  valve  stem,  and  its  periphery  rigidly  held  by  an 
air-tight  joint.  Under  the  diaphragm  is  a  small  space  that  is 
nearly  air-tight  and  is  of  the  same  diameter  as  the  free  part  of 
the  diaphragm.  Above  the  diaphragm  is  another  air  space  of  the 
same  diameter,  but  connected  with  the  passage  through  which 
the  air  is  drawn  to  the  motor.  When  air  is  drawn  into  the  motor 
the  reduction  of  pressure  above  the  diaphragm  by  suction 
allows  the  air  confined  in  the  space  below  the  diaphragm  to 
expand  and  lift  the  latter,  together  with  the  attached  valve,  so 
as  to  open  the  nozzle  and  allow  the  liquid  fuel  to  run  out  by 


54  THE  GAS  ENGINE 

both  suction  and  gravity,  or  by  suction  and  pressure  when  a 
pressure  fuel  tank  is  used.  The  amount  of  fuel  flowing  out  is 
adjusted  by  a  regulating  screw  against  which  the  valve  stem 
strikes  when  it  lifts. 

Throttle  control  and  a  spring-seated  air  valve  can  be  used  in 
this  type  of  carbureter. 


FIG.  31. 

Carbureter  Valve.     The  Lunkenheimer  Company,  Cincinnati,  Ohio. 

The  gasoline  is  fed  in  by  pressure  to  the  passage  around  the  needle  valve  20  and 
passes  through  a  small  orifice  to  the  conical  seat  of  the  main  valve  18.  The 
latter  is  pressed  against  its  seat  by  the  expansive  action  of  the  coil  spring  19. 
The  gasoline  orifice  is  closed  by  the  valve  18  when  the  latter  is  seated. 

The  suction  of  the  motor  at  the  lower  end  B  of  the  carbureter  draws  the  valve  18 
down  from  its  seat  so  that  air  enters  at  the  top  C  and  flows  down  past  the  valve. 
The  suction  and  gravity  (or  pressure)  both  cause  gasoline  to  flow  from  the  open 
nozzle  when  the  valve  18  is  drawn  from  its  seat  by  suction  and  air  is  passing 
through  the  carbureter.  The  flow  of  gasoline  is  regulated  by  the  needle  valve  20. 

27.  Spray  Carbureters  in  General.  —  Numerous  types  of  the 
spray  carbureter  other  than  those  described  above  are  in  more 
or  less  general  use.  The  nozzle  is  vertical  in  nearly  all.  In 
some  cases  it  is  slightly  inclined  from  the  vertical,  as  much  as 
forty-five  degrees  in  one  or  two  designs.  The  air  current  passes 
in  the  direction  that  the  nozzle  points  in  the  great  majority  of 
designs;  in  a  smaller  number  it  passes  across  the  nozzle  at  right 
angles  to  the  opening;  and  in  a  few  isolated  cases  it  comes  down 
against  the  orifice  of  the  nozzle. 

In  some  a  coil  of  wire  is  used  to  act  as  the  spring  air  valve 
already  mentioned  and  at  the  same  time  to  break  up  the  current 
of  air  so  as  to  make  the  mechanical  mixture  of  the  air  and  vapor 


CARBURATION  55 

more  complete  than  it  is  supposed  to  be  without  some  mixing 
device.  One,  a  recent  design,  has  a  cylindrical  wire  cage  at- 
tached to  one  end  of  a  propeller  wheel  and  the  whole  mounted 
on  a  central  spindle.  The  fuel  and  air  pass  through  the  pro- 
peller wheel  and  cage  after  coming  together  on  their  way  to  the 
motor.  The  current  of  air  and  vapor  causes  the  propeller  wheel 
and  cage  to  rotate  rapidly.  The  centrifugal  action  throws  any 
liquid,  such  as  water  or  unvaporized  fuel,  out  against  the  walls 
surrounding  the  cage,  and  a  dry  mixture  is  thus  secured. 


FIG.  32. 

Carbureter  Valve.     The  Lunkenheimer  Company. 

This  is  a  modified  form  of  Fig.  31.  Air  enters  at  the  lower  opening  C  and  the 
mixture  passes  out  at  the  upper  opening  B.  Gasoline  flows  in  at  5  and  follows 
a  duct  to  the  pocket  back  of  the  needle-valve  point.  The  lift  or  movement  of  the 
main  valve  F  is  regulated  by  the  screw-threaded  stem  extending  down  from 
the  wheel  3  at  the  top.  The  top  of  the  valve  strikes  against  and  is  stopped  by 
the  lower  end  of  this  stem. 

One  of  the  simplest  carbureters,  probably  the  simplest,  con- 
structed resembles  an  ordinary  globe  angle  valve  in  general 
appearance.  The  valve  is  pressed  against  its  seat  by  a  weak 
spring  that  allows  it  to  rise  when  the  suction  of  the  motor  acts  to 
draw  air  through.  A  liquid-fuel  supply  pipe  terminates  in  a 
small  orifice  in  the  conical  valve  seat.  When  the  valve  rests  on 


56  THE  GAS  ENGINE 

its  seat  the  orifice  is  closed  and  no  liquid  can  flow  into  the  air 
passage,  but  when  suction  lifts  the  valve  the  orifice  is  uncovered 
and  the  liquid  fuel  is  drawn  out  by  the  suction,  with  some  aid 
from  gravity  or  the  pressure  of  a  pressure  system  of  fuel  supply. 
The  liquid  is  vaporized  as  in  other  types  of  spray  carbureters. 
The  lift  of  the  valve  is  regulated  by  a  screw  above  it  that  occu- 
pies the  place  of  the  valve  stem  that  is  used  in  the  ordinary  angle 
valve.  The  intensity  of  suction  depends  on  the  lift  of  the  valve. 
The  latter  can  be  completely  closed  by  screwing  down  the  regu- 
lating screw.  There  is  a  needle  valve  in  the  fuel  supply  duct  for 
the  regulation  of  the  amount  of  fuel  delivered.  This  carbureter 
is  intended  for  use  only  on  motors  that  take  a  full  charge  for 
each  impulse  stroke.  It  has  proved  very  satisfactory  for  such 
service. 

28.  Other  Types  of  Carbureters  for  Naphtha  and  Gasoline.  — 
One  type  of  carbureter  that  was  much  used  at  one  time  but  is 
becoming  less  common  on  account  of  its  displacement  by  the 
spray  class,  has  a  considerable  surface  of  metal  on  which  the 
gasoline  or  naphtha  is  allowed  to  run  and  is  then  vaporized  by 
air  passing  over  it.  The  vaporizer  is  made  in  various  forms. 
One  is  a  cone  of  wire  gauze.  In  its  operation  the  liquid  is 
dropped  on  the  apex  and  runs  down  toward  the  base.  The  air 
is  drawn  up  through  the  gauze  and  rapid  vaporization  occurs. 
Instead  of  the  wire  gauze  a  conically  coiled  wire  or  a  piece 
of  perforated  metal  is  often  used.  Different  shapes  find 
application. 

In  the  earlier  forms  the  air  was  enriched  with  hydrocarbon 
vapor  to  the  saturation  point,  which  gave  a  practically  definite 
amount  of  fuel  per  cubic  foot  of  air,  and  then  the  saturated  mix- 
ture was  diluted  by  mixing  it  with  pure  air  until  the  ratio  of 
pure  air  and  hydrocarbon  vapor  became  suitable  for  complete 
combustion. 

In  most  of  the  later  types  the  liquid  fuel  is  directly  mixed  with 
the  air  passing  into  the  motor,  and  in  such  a  proportion  as  gives 
a  combustible  mixture.  The  proportion  of  the  liquid  fuel  is 
regulated  by  some  device  similar  in  its  general  action  to  those 
of  the  float-feed  and  disk-feed  carbureters. 


Air  Escape 


SECTION  B-B 


Fl 

Spray  Carbureter  with  Gasoline  and  Water  Nozzles.     C 
This  carbureter  is  provided  with  a  reservoir  for  water  as  well  as  one  for  gasoline. 

carbureting  chamber  or  pipe.      The  carbureter  is  double,  with  a  gasoline  noz; 

one  of  the  carbureting  chambers  and  its  nozzles  are  shown  in  the  figures. 
The  water  is  mixed  with  the  charge  to  cool  down  an  overheated  combustion  ct 
An  excess  of  gasoline  is  pumped  continuously  into  the  gasoline  reservoir  of  the  carbl 

allows  the  excess  gasoline  to  escape  and  maintains  a  nearly  constant  level  in  the 

constant  level  in  the  water  reservoir  of  the  carbureter  in  a  similar  manner. 
The  needle  valve  for  regulating  the  gasoline  (for  either  combustion  chamber)  is  set  1 

out  past  the  spring-closed  valve  (which  is  opened  by  the  suction  of  the  motor)  ar 
The  gasoline  nozzle  has  three  orifices. 
This  carbureter  was  used  on  a  four-cycle,  single-acting  motor  with  two  cylinders 


Air  Escapes 
HORIZONTAL  SECTION  A-A 


SECTION  G-G 


Water 


I 

/'""  '  ' 


SECTION  D-D 
Through  the  Water  Chamber 


Needle  Valve' 
for  control  of  water 
[RTICAL  SECTION  C-C  to  the  mature 

3. 

ant  Level  of  Gasoline  and  Water  by  Overflow  Method. 

as  separate  spray  nozzles  for  water  and  for  gasoline,  both  opening  into  the  same 

,  water  nozzle,  and  a  carbureting  chamber  for  each  combustion  chamber.      Only 

er  and  prevent  premature  ignition. 

:r  by  a  pump  driven  by  the  motor.     An  overflow  opening  in  the  carbureter  reservoir 

rvoir.      The  overflow  runs  back  to  the  supply  tank.      The  water  is  maintained  at  a 

•e  a  richer  mixture  than  is  to  be  used  in  the  motor.     This  over-rich  mixture  flows 
m  mixes  with  more  air  on  its  way  to  the  motor. 


6J  inches  diameter  of  bore,  and  with  a  piston  stroke  of  10  inches. 


CARBURATION  57 

29.  Cooling  Effect  of  Vaporization.  —  The  vaporization  of  a 
liquid  requires  heat.     When  the  liquid  fuel  is  vaporized  in  a 
spray  carbureter   the  necessary  heat  is  abstracted^from  the  air 
with  which  the  vapor  mixes,  and  from  the  metal  of  the  carbureter. 
Most  of  the  vaporization  takes  place  just  beyond  the  fuel  nozzle 
in  the  spray  carbureter.     As  a  result  the  metal  in  that  neighbor- 
hood becomes  very  cold.     It  is  not  unusual  to  find  it  covered 
with  frost  even  in  hot,  dry  weather,  but  this  occurs  to  a  more 
marked  extent  in   a  cool,   moist   atmosphere.     The  heat  con- 
ductivity of  the  metal  causes    the  entire  carbureter  to  become 
cold  and  chill  the  liquid  fuel  so  that  it  will  not  vaporize  so  readily. 
With  the  better  qualities,  or  more  correctly,  the  more  volatile 
fuels,  this  cooling  by  vaporization  does  not  need  much,  if  any, 
consideration  so  far  as  the  vaporization  is  concerned. 

But  frost  and  ice  not  infrequently  collect,  in  very  humid  or 
rainy  weather,  to  such  an  extent  that  the  inside  of  the  air  passage 
or  mixture  chamber  where  the  vaporization  occurs  becomes 
coated  with  frost  and  ice.  This  is  apt  to  interfere  with  the 
operation  of  the  throttle  valve,  or  even  to  obstruct  the  air  passage 
to  such  an  extent  as  to  affect  the  working  of  the  motor.  When 
the  poorer  or  less  volatile  grades  of  oil  are  used,  they  will  not 
always  vaporize  at  atmospheric  temperature  even  before  the 
carbureter  has  become  cooled. 

30.  Heating  the   Carbureter  or  the  Air.  —  In  order  to  pre- 
vent  the  formation  of  ice  in  the  carbureter,  and  to  make  it 
possible  to  use  the  lower  and  less  volatile  grades  of  naphtha  and 
gasoline,  either  the  air  is  heated  before  reaching  the  carbureter 
or  the    carbureter  itself  is  heated    by  a   hot-water  or  hot-oil 
jacket. 

The  hot-water  jacket  generally  extends  around  the  part  of  the 
air  passage  where  the  most  vaporization  occurs,  and  also  around 
the  carbureter  reservoir  when  a  float  is  used,  or  around  the 
portion  where  the  liquid  fuel  enters  the  carbureter  when  there 
is  no  float  reservoir.  The  hot  water  or  oil  for  jacketing  is  taken 
from  that  used  to  cool  the  motor  cylinder  when  the  latter  is 
liquid-jacketed.  The  liquid-warmed  carbureter  is  used  only  in 
connection  with  a  water-cooled  or  oil-cooled  motor. 


58  THE  GAS  ENGINE 

Preheating  the  air  before  it  passes  into  the  carbureter  is 
generally  accomplished  by  causing  it  to  pass  over  some  of  the 
heated  surface  of  the  motor  cylinder  or  exhaust  pipe.  The 
intake  pipe  frequently  has  one  branch  that  takes  in  preheated 
air,  and  another  that  receives  air  at  atmospheric  temperature. 
By  the  use  of  adjustable  valves  the  air  is  taken  in  through  either 
or  both,  as  desired. 

31.  Carbureters  for  Kerosene  and  other  Non-Volatile  Liquids. 
—  A  temperature  much  higher  than  that  of  the  atmosphere  is 
necessary  for  vaporizing  kerosene  and  others  of  the  heavier  dis- 
tillates of  petroleum.  In  the  very  numerous  designs  that  have 
been  used,  the  heat  for  raising  the  temperature  to  the  vaporiza- 
tion point  has  generally  been  taken  from  the  exhaust  gases  by 
passing  them  around  or  through  the  carbureter  in  passages 
provided  for  the  exhaust  gas.  The  chief  difficulty  met  has  been 
the  keeping  of  the  carbureter  at  a  proper  temperature  at  all 
loads  on  the  motor.  The  tendency  in  a  simple  form  of  car- 
bureter through  which  all  or  always  the  same  proportion  of  the 
exhaust  gases  pass,  is  for  the  carbureter  to  become  too  cool  on  a 
light  load  if  it  is  so  constructed  that  it  does  not  become  too  hot 
when  the  motor  is  working  at  about  its  full  capacity.  This 
type  of  carbureter  has  been  made  to  work  satisfactorily  on  launch 
and  boat  motors,  where  the  rate  of  power  generation  is  practically 
constant.  An  auxiliary  flame  is  required  for  keeping  the  car- 
bureter hot  when  the  motor  stops,  and  for  heating  it  before  start- 
ing after  the  parts  have  become  cold. 

When  the  temperature  is  kept  high  above  the  vaporization 
point  while  the  motor  works  at  full  load,  there  is  apt  to  be  trouble 
from  rapid  deterioration  of  the  metal  of  the  carbureter,  stoppage 
of  its  passages,  oxidation  of  the  metal  and  deposit  of  carbon  from 
the  fuel  and  exhaust  and  even  from  igniting  the  mixture  while  it 
is  still  in  or  near  the  carbureter. 

Some  of  the  kerosene  carbureters  make  a  saturated  mixture  of 
air  and  fuel  vapor  at  a  temperature  well  above  the  vaporization 
point  of  the  kerosene,  and  afterward  dilute  it  with  air,  thus 
securing  a  combustible  mixture  without  an  excessive  temperature 
of  the  entering  charge.  The  heat  of  compression  and  that 


CARBURATION  59 

received  from  the  cylinder  walls  are  relied  upon  to  keep  the 
kerosene  in  the  vapor  state  until  combustion  occurs. 

The  adjustment  and  handling  of  a  kerosene  carbureter  when 
in  operation  cannot  be  so  readily  and  conveniently  accomplished 
as  with  one  for  gasoline,  naphtha,  and  alcohol,  on  account  of  the 
necessarily  high  temperature  of  the  kerosene  carbureter.  Adjust- 
ing screws  and  minute  parts  are  injured  by  the  heat,  which  also 
opens  joints  and  causes  leakage.  On  the  whole,  the  problem 
of  making  a  successful  kerosene  carbureter  is  far  more  difficult 
than  to  make  one  for  naphtha  or  alcohol.  The  result  is 
that  the  general  tendency  is  to  eliminate  the  use  of  the  kero- 
sene carbureter  by  injecting  the  liquid  fuel  directly  into  the 
combustion  space  of  the  motor  and  to  vaporize  as  well  as  burn 
it  there. 

32.  Early  and  Obsolete  Forms  of  Carbureters.  —  One  of  the 
early  methods  of  carbureting  the  air  for  internal-combustion 
motors  was  to  pass  it  more  or  less  directly  through  the  liquid  fuel, 
as  from  the  submerged  opening  of  an  air  pipe  partly  immersed  in 
the  liquid.  The  bubbles  of  air,  rising  up  through  the  liquid, 
became  more  or  less  completely  saturated  with  the  vapor  of  the 
liquid.  Heat  was  added  to  the  less  volatile  liquids  to  bring  them 
up  to  the  vaporization  temperature. 

Another  method  was  to  blow  air  down  against  the  surface  of 
the  liquid  so  as  to  agitate  it  and  absorb  its  vapor. 

The  above  two  methods  are  still  applied  to  a  small  extent  in 
the  carbureters  for  kerosene  and  others  of  the  less  volatile  liquids. 
It  is  difficult  in  them,  almost  impossible  in  fact,  to  secure  the 
proportions  of  an  economical  combustible  mixture  in  this  manner. 
The  usual  method  of  using  them,  therefore,  is  to  make  a  saturated 
or  over-rich  mixture  and  then  dilute  it  with  air  to  the  desired 
proportions. 

Still  another  early  method  was  to  drop  or  flow  the  liquid  fuel 
on  an  absorbent  piece  of  cloth  or  other  textile  fabric,  cotton  or 
woolen  wicking,  or  the  waste  fiber  from  textile  mills.  The  air 
was  passed  through  the  fabric  or  waste  and  thus  became  car- 
bureted. The  cloth  or  fibers  gradually  became  fouled  by  dust 
carried  in  by  the  air,  and  in  some  cases  by  deposits  from  the 


60  THE   GAS   ENGINE 

liquid.  The  rate  of  carburation  therefore  changed,  and  the 
fabric  had  to  be  renewed. 

The  capillary  action  of  wicks  was  also  utilized  by  placing 
them  partly  in  the  liquid  with  one  end  extending  into  the  air 
passage,  so  that  the  fluid  that  crept  up  the  wick  was  vaporized 
and  carried  off  by  the  air.  The  use  of  animal  and  vegetable 
fibers  in  any  form  for  carburation  seems  to  have  been  dis- 
continued completely  in  connection  with  internal-combustion 
motors. 

33.   Effect  of  Preheating  the  Charge  on  the  Power  of  the  Motor. 

-  The  amount  of  power  that  is  developed  in  the  motor  from  a 
combustible  charge  of  a  given  composition  is  almost  directly 
proportional  to  the  "weight  of  the  charge  when  the  cylinder  is 
always  filled  to  the  same  pressure  before  compression  begins.  If 
a  charge  enters  at  a  high  temperature  it  will  have  less  weight  (for 
the  same  volume)  than  one  that  is  cool  when  it  enters.  This 
assumes  that  both  charges  pass  in  through  the  same  passages 
without  any  change  in  the  area  or  form  of  the  opening  in  any 
place.  Under  this  condition  the  pressure  in  the  motor  cylinder 
at  the  completion  of  charging  will  be  the  same  in  both  cases.  The 
reduced  weight  of  the  hot  charge  means  a  corresponding  reduction 
of  the  fuel  to  be  transformed  into  heat,  and  consequently  less 
power  developed. 

From  the  above  it  can  be  seen  that,  while  preheating  the  air 
is  in  many  cases  advisable,  or  even  necessary,  to  secure  vaporiza- 
tion and  prevent  freezing  of  the  carbureter  on  .-account  of  the 
vaporization,  it  should  not  be  carried  to  a  higher  temperature 
than  necessary  if  maximum  power  from  the  motor  is  desired. 
The  reduction  of  power  capacity  of  the  motor  is  one  of  the  objec- 
tions to  the  kerosene  carbureter  with  its  highly  preheated  air. 

The  mixture  from  a  gasoline  or  naphtha  carbureter  that  is  not 
jacketed  by  hot  water,  hot  gases,  etc.,  and  takes  its  air  at  atmos- 
pheric temperature,  is  much  cooler  than  the  atmosphere  when  it 
enters  the  motor.  This  is  one  of  the  reasons  why  a  motor  running 
on  naphtha  fuel  will  develop  more  power  than  when  on  gas  fuel, 
even  though  the  heat  value  of  a  pound  of  the  mixture  is  the  same 
in  both  cases. 


CARBURATION  6 1 

• 
Fuel  Supply  for  Carbureters. 

34.    Gravity,  Compression,  and  Pump  Supply  of  Fuel.  —  The 

liquid  fuel  for  a  carbureter  is  either  placed  in  a  tank  at  a  level 
higher  than  that  of  the  carbureter  and  flows  down  to  the  car- 
bureter by  gravity,  or  the  supply  tank  is  placed  lower  than  the 
carbureter  and  the  liquid  forced  up  by  compressed  air,  gas  or 
vapor,  or  by  a  pump. 

In  the  gravity  system  the  tank  should  have  a  minute  opening 
or  vent  at  the  top  so  that  air  can  enter  it  as  the  fuel  flows  out. 
If  this  opening  is  not  provided,  the  partial  vacuum  produced  by 
the  flowing  out  of  the  liquid  will  first  retard  and  finally  stop  the 
flow.  A  very  minute  hole  is  sufficient  for  the  vent,  but  it  should 
be  large  enough  not  to  be  easily  clogged.  About  one-thirty- 
second  of  an  inch  in  diameter  is  the  size  generally  used. 

The  pipe  from  the  gravity  supply  tank  to  the  carbureter 
should  not,  under  any  condition,  have  large  vertical  bends  or 
any  part  much  lower  than  the  carbureter.  Vertical  bends  or  a 
low  pipe  is  apt  to  cause  an  air  lock  that  will  prevent  the  liquid 
from  flowing  into  the  carbureter  after  it  has  been  drained  or 
otherwise  emptied,  or  when  the  supply  tank  is  filled  after  being 
completely  empty. 

In  the  compression  system  of  fuel  supply,  air  is  forced  into  the 
supply  tank  after  it  has  been  nearly  filled  with  fuel.  After  the 
motor  is  started  the  pressure  is  maintained  in  the  tank  by 
the  exhaust,  frpm  the  motor.  A  common  method  of  doing  this 
in  automobile  practice  is  to  make  a  pipe  connection  between  the 
supply  tank  and  the  exhaust  pipe  of  the  motor.  The  connection 
to  the  exhaust  pipe  is  made  very  close  to  the  motor.  A  check 
valve  is  placed  in  the  connecting  pipe,  generally  near  the  motor, 
which  is  the  proper  location.  The  back  pressure  of  the 
exhaust  at  the  instant  of  its  discharge  is  sufficient  to  force  some 
of  the  exhaust  gases  past  the  check  valve  and  into  the  fuel  tank. 
The  connecting  pressure  pipe  must  be  of  small  diameter  in  order 
to  prevent  the  passage  of  a  flame  through  it  from  the  motor  to 
the  tank  in  case  the  pipe  should  ever  become  filled  with  com- 
bustible mixture.  It  may  at  first  seem  that  there  is  a  probability 


62  THE  GAS  ENGINE 

of  combustible  mixture  passing  into  the  pipe  when  the  motor 
misses  an  explosion  in  the  cylinder  to  which  the  compression  pipe 
is  connected.  But  there  is  really  little  danger  of  this,  since  there 
is  no  pressure  in  the  combustion  cylinder  at  the  time  of  opening 
the  exhaust  valve  after  a  misfire. 

The  use  of  a  pump  to  lift  the  fuel  is  confined  chiefly  to  station- 
ary motors,  but  a  pump  is  used  to  some  extent  on  portable 
and  semi-portable  motors.  In  stationary  motors  the  fuel  is  very 
conveniently  stored  in  the  base  of  the  motor.  The  plunger 
type  of  pump  is  generally  used  for  this  purpose,  and  is  driven 
by  the  motor  itself,  of  which  it  usually  forms  a  part. 


CHAPTER    III. 
IGNITION. 

35.  General.  —  The  manner  in  which  a  charge  is  ignited  in 
an  oil  motor  whose  charge  of  fuel  is  injected  in  the  liquid  form, 
has   already  been   discussed   in   connection   with   the   different 
types  of  oil-burning  motors. 

The  electric  spark  or  electric  arc  has  come  into  almost  uni- 
versal use  for  igniting  the  combustible  charge  when  it  is  neces- 
sary to  have  some  source  of  heat  for  this  purpose  other  than  that 
necessary  to  vaporize  an  injected  liquid  fuel,  as  in  the  oil-burning 
motors.  High-tension  ignition,  also  called  jump-spark  igni- 
tion, systems  use  a  spark  passing  across  the  gap  between  two 
permanently  separated  metallic  points.  In  low-tension  arc- 
ignition  systems,  an  electric  arc  is  drawn  at  the  instant  a  break 
is  made  in  the  electric  circuit  by  separating  a  pair  of  metallic 
contact  points. 

A  hot  piece  of  metal,  porcelain,  or  other  substance  with  which 
the  combustible  mixture  is  brought  into  contact,  is  still  used  to 
some  extent,  however.  One  of  the  early  methods  was  to  bring  a 
flame  into  contact  with  the  mixture  at  the  moment  it  was  to  be 
ignited.  This  is  practically  obsolete.  The  constantly  burning 
flame  of  the  Bray  ton  motor  has  already  been  discussed. 

36.  Double  Ignition.  —  Two  entirely  separate  ingition  systems 
are  used  in  many  of  the  better  small  motors,  and  quite  commonly 
in  large  ones.      In  automobile  and  launch  motors  both  the  high- 
tension    (jump-spark)   and  the  low-tension    (arc)   systems    are 
installed.     In  large  stationary  motors  the  two  systems  are  gen- 
erally duplicates. 

It  is  quite  common  practice  to  operate  both  ignition 'systems 
at  once  in  large  motors,  but  this  is  not  usual  in  the  smaller  ones. 
In  the  latter  case  one  system  is  generally  held  as  a  reserve. 

63 


64  THE   GAS  ENGINE 

37.  Low-Tension  Electric- Arc  Ignition.  —  This  is  often  called 
either  the  "  make-and-break "  or  the  "  break-and-make "  system, 
since  the  electric  circuit  is  completed  and  broken  each  time  an 
arc  is  formed. 

A  low-voltage  electric  current  of  a  few  amperes  flows  through 
an  insulated  metal  rod  that  pierces  the  wall  of  the  combustion 
chamber,  in  the  arc  system  of  ignition.  A  movable  metal  con- 
tact, electrically  connected  with  the  metal  of  the  motor,  presses 


FIG.  34. 
Ignition  Points.     Low-Tension  Make-and-Break. 

The  stationary  contact  point  (ring)  D  and  the  rod  that  supports  it  are  insulated 
from  the  remainder  of  the  complete  igniter. 

The  contact  ring  C  oscillates  about  the  upper  spindle  and  is  brought  into  contact 
with  D  just  before  the  time  for  ignition,  and  immediately  separated  from  it  to 
draw  an  arc.  C  and  the  parts  attached  to  it  are  not  insulated  from  the  main 
part  of  the  apparatus  or  from  the  metal  of  the  motor  when  the  igniter  is  in  place. 

periodically  against  the  inner  end  of  the  insulated  rod.  The 
electric  connection  between  the  movable  contact  part  and  the 
metal  of  the  motor  is  generally  made  by  the  very  simple  means  of 
not  insulating  it  from  the  cylinder  where  it  pierces  the  latter's 
wall.  The  stationary  and  moving  igniter  rods  both  generally 
enter  the  cylinder  through  a  removable  plate  or  plug  that  forms 
part  of  the  cylinder  wall  when  in  place.  The  insulated  rod  and 


IGNITION  65 

the  metal  of  the  motor  cylinder  are  respectively  connected  to  the 
terminals  of  the  source  of  electric  supply.  The  separation  of  the 
contact  points  inside  the  combustion  cylinder  draws  an  electric 


/K 


FIG.  35. 

Make-and-Break  Igniter  in  Place. 

The  igniter,  Fig.  34,  is  here  shown  in  place  on  the  motor.  The  contact  points  are 
inside  a  chamber  which  forms  part  of  the  combustion  space  of  the  motor.  F  is 
the  lay  shaft  (half-speed  shaft)  of  the  motor.  The  lay  shaft  rotates  so  that  the 
top  moves  out  from  the  paper  on  which  the  illustration  is  printed.  The  projec- 
tion on  E  engages  with  the  spring  I  as  F  rotates  and  thus  brings  the  contact 
point  C  up  against  the  stationary  point  D.  Further  rotary  movement  of  E  allows 
7  to  become  disengaged  from  the  projection  on  E  and  to  snap  back  so  as  to 
quickly  separate  the  contact  points  and  draw  an  arc. 

arc  that  ignites  the  combustible  gaseous  mixture  surrounding 
them. 

In  the  "make-and-break"  system  the  contact  points  are  brought 
together  and  immediately  separated  to  draw  the  arc. 

The  "  break-and-make  "  method  is  to  keep  the  contact  points 
together  constantly  except  during  the  short  interval  that  lies 
between  their  separation  and  almost  immediate  bringing  into 
contact  again. 

A  minimum  amount  of  electric  energy  is  consumed  in  the 
make-and-break  system,  and  injurious  heating  of  the  contact 
points  is  hardly  possible.  There  is  a  maximum  opportunity  for 
carbon  and  oil  to  collect  on  the  contact  points,  however,  and  foul 
them  so  that  they  cannot  come  into  electric  contact  when  brought 
together  mechanically. 


66 


THE   GAS  ENGINE 


There  is  less  liability  to  failure  of  the  formation  of  the  arc  in 
the  break-and-make  system  on  account  of  fouling  of  the  contacts, 
but  it  requires  more  electric  energy  if  the  source  of  electric  supply 
continuously  delivers  current  at  a  uniform  rate  while  the  contacts 
are  together,  but  not  a  larger  current  than  is  required  by  the 
make-and-break  system.  There  is  a  greater  tendency  in  the 
break-and-make  system  than  in  the  other  to  heat  the  contacts 
when  current  flows  during  the  entire  time  the  circuit  is  closed 


FIG.  36. 
Double  Make-and-Break  Igniter. 

at  the  contacts.  Injurious  heating  by  the  current  seldom  occurs, 
however,  in  an  electric  arc  ignition  system  that  is  properly 
designed  and  operated. 

To  secure  the  advantage  of  the  greater  certainty  of  closing 
the  circuit  at  the  contact  points  than  belongs  to  the  break-and- 
make  system,  and  at  the  same  time  keep  the  liability  of  heating 
as  low  as  it  is  in  the  make-and-break  system,  special  forms  of 
electric  generators  are  used.  These  generators  produce  current 
intermittently  and  during  only  a  short  period  covering  the  instant 
that  the  contacts  separate  to  draw  the  arc. 

Metals  and  alloys  having  a  high  fusing  point  were  thought 
necessary  and  were  used  exclusively  in  the  early  application  of 
electric-arc  ignition.  Platinum,  iridium,  and  platinum-iridium 
alloy  were  generally  used.  Platinum  and  iridium  are  so  costly 


IGNITION  67 

as  to  make  it  desirable  to  substitute  less  expensive  materials  for 
them.  They  have  been  almost  completely  displaced  by  steel 
alloy  contacts,  which  give  better  service,  under  the  modern 
methods  of  using  them,  than  the  more  expensive  metals  pre- 
viously used.  It  has  been  found  that  there  is  no  necessity  to 
form  the  contacts  into  a  point  or  anything  approaching  a  point 
in  form.  Blunt  ends  and  flat  or  nearly  flat  surfaces  are  in 
common  and  entirely  successful  operation.  One  form  that  has 
given  entire  satisfaction  has  a  broad  steel  ring,  resembling  a 
washer,  attached  securely  to  the  end  of  the  insulated  rod,  and 
another  similar  ring  fastened  to  the  moving  part  inside  the 
cylinder.  The  axes  of  the  rings  are  more  or  less  perpendicular 
to  each  other,  and  their  edges  are  brought  together  to  close  the 
circuit.  If  a  ring-shaped  contact  piece  becomes  worn  or  pitted 
by  fusing,  it  can  be  turned  around  slightly  on  its  support  so  as 
to  bring  a  new  portion  of  its  edge  into  action.  Nickel  steel 
alloy  has  been  found  good  for  contacts,  along  with  other  kinds 
of  steel. 

The  insulating  material  for  the  stationary  ignition  rod  that 
pierces  the  wall  of  the  cylinder  is  subjected  to  a  high  temperature 
and  must,  therefore,  be  of  a  nature  that  will  withstand  the  heat 
and  retain  its  insulating  properties.  Mica,  lava,  porcelain,  and 
asbestos  are  the  materials  generally  used.  The  asbestos  is  more 
especially  used  as  a  packing  for  the  other  materials.  The  mica 
is  used  in  thin  pieces,  stamped  or  cut  to  suitable  form  and  laid 
against  each  other.  The  joints  must  be  made  with  care,  since  the 
expansion  and  contraction  due  to  heating  and  cooling  of  the 
cylinder  tend  to  open  them  and  allow  the  escape  of  gas,  especially 
at  the  time  when  the  pressure  is  high  during  and  just  after  com- 
bustion. 

The  spindle  carrying  the  movable  contact  point  generally  has 
an  oscillatory  motion  in  the  cylinder  wall,  so  as  to  give  a  rocker- 
arm  motion  to  the  arm  that  carries  the  contact  piece.  In  some 
designs,  however,  the  spindle  has  a  rotary  motion.  There  is 
ordinarily  no  difficulty  met  in  keeping  a  tight  joint  at  the  place 
where  the  rocker  arm  pierces  the  cylinder  wall.  The  pressure 
of  the  confined  gases  forces  the  shoulder  or  collar  of  the  spindle 


68 


THE   GAS  ENGINE 


against  the  inner  surface  of  the  cylinder  wall,  and  thus  keeps  the 
joint  tight  if  the  bearing  surfaces  are  true. 

In  one  type  the  contact  points  are  pressed  together  by  the 
action  of  a  spring  connected  to  the  external  part  of  the  rocker 
shaft,  either  directly  or  by  means  of  an  outside  rocker  arm.  The 


FIG.  37. 

Make-and-Break  Igniter  with  Rotary  Contact  Piece. 

The  stationary  contact  piece  B  is  insulated  from  the  frame  of  the  motor  and  from 
the  outer  metallic  bushing  that  surrounds  the  middle  portion  of  B.  The  contact 
point  A  is  rotated  by  the  motor  at  half  the  speed  of  the  crank  shaft  for  a  four- 
cycle motor,  and  makes  contact  with  B  at  every  revolution. 

contacts  are  separated  at  the  proper  instant  by  the  action  of  a 
single-lobe  cam  on  a  shaft  that  rotates  at  the  same  speed  as  the 
crank  shaft  in  a  two-cycle  motor  and  at  half  the  speed  of  the 
crank  shaft  in  a  four-cycle  motor.  This  refers  to  one  cylinder  of 
a  single-acting  motor.  The  cam  acts  through  a  system  of  rods  and 
levers  that  transmit  the  motion  of  its  follower  to  the  movable  arm 
of  the  igniter. 


IGNITION 


69 


In  order  to  secure  a  very  rapid  separation  of  the  'contact  parts, 
a  "  hammer-blow "  device  is  sometimes  used.  The  rocker  arm 
of  the  igniter  supports  a  comparatively  heavy  part,  the  hammer, 
that  is  free  to  rotate  on  it.  The  parts  that  move  the  igniter  press 
the  hammer  back  against  the  resistance  of  a  spring  while  the  con- 
tact points  remain  together.  The  hammer  is  then  released,  and 
the  spring  throws  it  back  quickly.  It  strikes  an  arm  that  is 
rigidly  connected  to  the  rocker  shaft  of  the  igniter  point  with  a 
blow  that  forces  the  contacts  apart  almost  instantly.  The  rapid 

4 


FIG.  38. 

Rotor  of  Make-and-Break  Igniter. 

The  rotary  contact  part  of  the  igniter  shown  in  the  preceding  figure  has  a  graphite 
bearing,  shown  in  black,  for  the  rotating  spindle  2.  This  eliminates  the  necessity 
of  lubrication  with  oil,  since  the  graphite  is  a  solid  lubricant.  The  graphite  is 
not  an  insulator. 

separation  reduces  the  fusing  action  of  the  arc,  as  compared  with 
that  of  slow  opening,  by  breaking  the  arc  almost  as  soon  as  it  is 
formed.  Modern  practice  does  not  seem  to  show  any  necessity 
of  breaking  the  circuit  and  the  arc  any  more  rapidly  than  can  be 
done  with  the  simpler,  direct-acting  arrangement  more  generally 
used. 

38.  Sources  of  Electric  Supply  for  Ignition.  —  An  electric 
generator  is  the  best  source  of  supply  for  the  low-tension  arc 
system  of  ignition.  The  current  provided  must  be  flowing  as 
a  direct  current  at  the  instant  of  separating  the  contact  points 
and  drawing  the  arc  at  the  igniter.  The  nature  of  the  current 
at  other  times  when  the  circuit  is  closed  is  immaterial  (except 
that  it  must  not  be  large  enough  to  injure  the  apparatus). 


THE  GAS  ENGINE 


It  may  be  either  direct  continuous  or  pulsating,  intermittent  or 
alternating.  Generators  that  are  used  solely  for  this  purpose, 
and  are  practically  a  part  of  the  motor  accessories,  are  in  com- 
mon use.  Both  magneto-generators  and  those  with  electrically 
excited  magnetic  fields  are  suitable.  The  former  has  the 
advantage  of  being  less  complicated,  but  is  more  bulky  and 
generally  heavier  than  the  electrically  magnetized  type.  When 
the  electric  generator  is  suited  to  its  work,  one  of  its  terminals 
is  connected  directly  (electrically)  to  the  insulated  rod  that 
carries  the  stationary  contact  point,  and  the  other  terminal  of 


FIGS.  39  AND  40. 
Magneto  with  Shuttle- Wound  Armature.     Alternating-current  Type. 

1.  Permanent  magnets.  3.    Armature  core. 

2.  Armature.  4.    Armature  shaft. 

5,  6.  Insulated  slip  rings  to  which  the  two  terminals  of  the  armature  winding  are 
connected  and  on  which  the  brushes  bear  for  carrying  the  current  away 
from  the  magneto. 

The  armature  wire  is  wound  around  the  neck  that  connects  the  two  convexed  ends 
(or  sides)  of  the  core. 

the  generator  is  "grounded"  by  connecting  it  (electrically)  to 
the  metal  of  the  motor  at  any  convenient  place.  It  will  not 
give  more  current  when  thus  short-circuited  than  it  and  the 
contacts  in  the  cylinder  can  safely  carry.  In  some  cases  the 
moving  part  of  the  generator  rotates  at  a  speed  either  constant 
or  proportional  to  that  of  the  motor;  in  others  it  is  either 


IGNITION  71 

oscillated  or  moved  intermittently  and  always  in  the  same  direc- 
tion of  rotation. 

Direct  continuous  current  generators  and  direct  intermittent 
current  generators  are  the  types  generally  used  for  low-tension 
ignition.  The  direct  continuous  current  generator  is  distin- 
guished from  others  by  its  commutator  of  numerous  (copper) 
segments. 

The  type  of  generator  commonly  known  as  alternating  can 
be  operated  so  as  to  give  current  which  does  not  change  its 
direction  during  the  period  for  drawing  the  arc.  This  method 
of  operating  is  described  in  sections  40  and  41. 

In  variable-speed  motors,  direct-current  rotary  electric  gen- 
erators for  low-tension  (arc)  ignition  are  in  a  few  cases  driven 
at  a  speed  proportional  to  that  of  the  crank  shaft.  They  are 
specially  wound  so  as  to  give  enough  current  for  ignition  at  the 
lowest  speed  of  the  motor,  and  not  to  give  excessive  current,  or 
to  burn  out  on  account  of  high  voltage,  at  the  highest  speed  of 
the  motor.  It  is  more  usual,  however,  for  the  generator  to  be 
driven  through  a  friction  clutch  which,  is  thrown  partly  out  of 
engagement  at  a  certain  speed  that  is  the  maximum  predeter- 
mined for  the  generator.  Friction-pulley  drives  are  also  used 
to  limit  the  speed  in  a  similar  manner.  The  armature  of  the 
generator  thus  driven  never  exceeds  a  certain  speed,  but  main- 
tains it  when  the  motor  runs  at  its  slowest  speed.  Generators 
of  this  class  will  give  an  arc  hot  enough  to  ignite  the  charge  in 
the  combustion  chamber  at  the  speed  that  a  small  motor  can  be 
cranked  by  hand.  The  generator  is  therefore  all  that  is  neces- 
sary to  supply  electric  energy  for  ignition  purposes. 

An  electric  battery  of  dry  cells,  or  a  storage  battery,  can  be 
used  for  low-tension  arc  ignition.  The  battery  runs  down 
rapidly,  however,  even  when  the  make-and-break  system  is  used, 
as  distinguished  from  the  break-and-make.  A  "kick  coil," 
also  called  a  "choke  coil,"  should  be  used  in  the  battery  circuit 
to  draw  a  longer  and  stronger  arc  by  its  inductive  action  than 
can  be  produced  by  the  battery  without  it.  The  choke  coil  is 
made  by  winding  a  considerable  number  of  turns  of  insulated 
copper  wire  around  a  soft-iron  core.  The  core  is  usually  made 


72  THE   GAS  ENGINE 

up  of  a  number  of  small  rods  or  short,  straight  pieces  of  soft 
iron  wire  gathered  into  a  sheaf  or  bundle.  The  axis  of  the 
bundle  coincides  with  that  of  the  copper  coil. 

The  chief  use  of  the  battery,  in  connection  with  low-tension 
ignition,  is  for  starting  the  motor.  The  generator  can  be 
switched  on  for  continued  use. 

When  both  a  storage  battery  and  a  generator  are  thus  used 
for  igniting  purposes  they  can  be  so  connected  together  that  the 
generator  always  keeps  the  battery  charged  and  ready  for  use. 
The  latter  is  thus  always  a  reserve  factor  to  be  brought  into  use 
in  case  the  generator  fails.  This  method  is  known  as  "  floating 
the  battery  on  the  line." 

39.  Low-Tension  Arc  Igniter  with  Solenoid  Circuit  Breaker.  - 
This  igniter  differs  from  the  ones  of  the  type  just  described  in 
that  it  does  not  require  the  motor  to  have  as  a  part  of  its  mechan- 
ism proper  any  device  for  separating  the  contact  points.  Their 
separation  is  accomplished  by  the  magnetic  action  of  a  current 
passed  through  a  solenoid  coil  that  forms  part  of  each  spark 
plug.  The  igniter  is  compact  in  form  and  size.  It  screws  into 
a  hole  in  the  cylinder  wall.  T^he  hole  is  generally  of  the  standard 
size  for  a  half-inch  gas  pipe.  A  wire  from  the  electric  generator 
connects  to  its  one  binding  post.  The  "  grounding"  of  the 
outer  casing  of  the  plug  is  accomplished  by  screwing  it  into  the 
metal  of  the  cylinder.  This  completes  the  electric  circuit,  since 
the  second  terminal  of  the  generator  is  also  "grounded"  to  the 
metal  of  the  motor.  In  general  appearance  the  plug  resembles 
the  common  form  of  high-tension  spark  plug  to  be  described 
later. 

When  no  current  is  passing  through  the  solenoid  the  soft- 
iron  movable  core  is  forced  out  by  a  spring,  so  that  its  end  presses 
against  a  metal  bridge  that  spans  the  open  end  of  the  core  space 
of  the  coil.  The  metal  bridge  is  a  part  of  the  outer  shell  that  is 
threaded  to  screw  into  the  cylinder.  When  a  current  is  passed 
through  the  solenoid  its  core  is  drawn  in  against  the  resistance 
of  the  spring  and  away  from  contact  with  the  bridge.  The 
path  of  the  current  is  through  the  contact  points  before  they  are 
separated,  so  that  their  separation  draws  an  arc  between  the  end 


IGNITION  73 

of  the  solenoid  core  and  the  bridge.     The  arc  ignites  the  com- 
bustible gases  in  the  cylinder. 

An  electric  generator  especially  designed  to  supply  current  to 
the  arcing  plug  is  used  with  it.  A  timer  on  the  generator  closes 
the  circuit  to  each  plug  in  a  multi-cylinder  motor  at  the  proper 
moment,  and  delivers  current  to  it  long  enough  to  separate  the 
contact  points  and  draw  the  arc.  A  drop  of  heavy  oil  on  the 
contact  points  does-  not  prevent  the  formation  of  the  arc  when 
the  contacts  are  separated,  although  the  oil  still  connects  the 
points.  This  system  can  be  readily  installed  on  a  motor  that 
has  no  mechanism  for  separating  the  contact  points. 

40.    Oscillating  Electric  Generator  for  Low-Tension  Ignition. 
-  There  are  three  features  that  are  desirable  in  a  low-tension 
arc-ignition  system.     They  are: 

T.    Contact   points   kept  pressed    together   except  during  the 
instant  the  arc  is  drawn; 

2.  Current  supplied  only  when   needed  at  the  time  that  the 

contacts  are  separated  to  draw  the  arc; 

3.  An  electric    generator,  operated    entirely  by  the    motor, 

that  will  supply  the  right  amount  of  current  what- 
ever the  speed  of  the  motor,  and  also  when  the  motor 
is  moving  very  slowly,  as  when  "cranking"  a  small 
motor  by  hand,  or  "barring"  a  heavy  motor  to  start  it. 

By  the  use  of  an  electric  generator  which  produces  an  inter- 
mittent current  a  system  embodying  these  desirable  features  has 
been  evolved  and  is  in  general  use. 

In  the  oscillating  generator  the  armature  never  makes  a 
complete  rotation,  and  the  oscillations  of  the  armature  are 
intermittent.  The  armature  is  forced  to  one  extremity  of  its 
oscillation  by  a  spring. 

When  the  motor  is-  running,  the  armature,  oscillator,  or  rotor  is 
slightly  rotated,  through  a  fraction  of  a  revolution,  against  the 
resistance  of  the  spring,  at  a  comparatively  slow  rate,  by  a  cam, 
pin,  or  other  device  moving  in  unison  with  the  motor  shaft.  Just 
before  the  time  for  separating  the  contact  points  the  armature 


74 


THE   GAS  ENGINE 


is  released  and  snaps  back  by  the  action  of  the  spring.  This 
motion  is  rapid  enough,  and  through  a  sufficient  part  of  a  revolu- 
tion to  generate  enough  current  to  make  an  electric  arc  hot  enough 
to  ignite  the  charge  when  the  contacts  inside  the  combustion 
chamber  are  separated.  The  separation  of  the  contacts  is  gen- 
erally done  by  mechanism  connected  to  the  armature  or  oscillator 
so  as  to  move  in  unison  with  it.  The  separation  is  made  when 
the  current  is  at  or  near  its  maximum.  The  contacts  come 


FIG.  41. 

Position  of  the  armature  of  the  magneto  at  which  no  electromotive  force  and  current 
are  generated  during  its  rotation  or  oscillation.  The  arrows  indicate  the  direction 
of  flow  of  magnetism,  or  magnetic  flux. 

together  again  almost  instantly,  but  no  appreciable  current  passes 
through  them  till  the  armature  is  again  snapped  over.  The 
motion  of  forcing  the  armature  over  against  the  resistance  of  the 
spring  is  so  slow  that  no  appreciable  current  is  produced. 

The  amount  of  current  generated  and  the  intensity  of  the  arc 
do  not  in  any  manner  depend  on  the  speed  of  the  motor.  Even 
if  the  motor  is  not  rotating,  a  charge  can  be  ignited  by  this  device 
by  drawing  over  the  armature  and  allowing  it  to  snap  back.  The 
motor  can  be  started  from  rest  in  this  manner  if  the  piston  is  in 


IGNITION 


75 


position    for  the  impulse  stroke  and  the  cylinder  charged  with 
combustible  mixture. 

Generators  of  this  type  generally  have  permanent  field  magnets. 
Electromagnets  can  be  used,  but  the  necessity  of  maintaining  a 
source  of  electric  current  supply  is  generally  a  sufficient  reason 
for  not  using  them.  The  armature  may  be  made  stationary  out- 
side the  field  magnet,  which  is  then  made  small  and  mounted  so 
as  to  oscillate  in  the  manner  already  described. 


FIG.  42. 

Position  of  magneto  armature  at  about  which  the  voltage  and  current  generated  by 
a  uniform  speed  of  rotation  are  a  maximum.  When  the  armature  rotates  at  a 

.  uniform  speed  from  the  position  of  Fig.  41  to  that  of  Fig.  42,  the  pressure  (and 
current  if  the  external  circuit  is  kept  closed)  keep  increasing  till  a  maximum  of 
each  is  reached  at  about  the  position  of  Fig.  42.  The  maximum  value  of  the 
current  lags  somewhat  behind  that  of  maximum  pressure  when  the  external  cir- 
cuit is  kept  closed. 

In  a  variable-speed  motor,  as  one  on  an  automobile,  the 
separation  of  the  contact  points  will  not  always  occur  when  the 
piston  is  in  the  same  position.  This  is  because  the  time  interval 
between  the  release  of  the  armature  and  the  separation  of  the 
contacts  in  the  cylinder  is  always  the  same  whatever  the  speed 


76  THE   GAS  ENGINE 

of  rotation  of  the  motor.  If  the  release  is  made  when  the  crank 
is  on  the  dead  center  and  the  piston  just  ready  to  begin  its  impulse 
stroke,  the  contacts  will  not  separate  until  the  piston  has  moved 
out  some  on  its  stroke.  The  distance  that  the  piston  moves  out 
will  be  greater  the  higher  the  speed. 

Some  means  of  readily  adjusting  the  time  of  release  of  the 
armature  while  operating  the  motor  is  therefore  desirable  on  a 
variable-speed  motor,  and  is  generally  provided.  Such  a  quick 
means  of  adjustment  is  not  needed  on  a  constant-speed  motor, 
but  some  means  of  setting  the  release  to  the  best  position,  where 
it  is  to  remain  permanently  as  long  as  the  same  fuel  is  used  and 
the  demands  for  power  do  not  change  greatly,  is  desirable. 

41.  Generator  with  Interrupted  Magnetic  Circuit,  for  Low- 
Tension  Intermittent  Current.  —  A  very  simple  device  for  gener- 
ating electric'  current  intermittently  as  required  for  ignition  in 
an  internal-combustion  motor  finds  application  to  some  extent. 
It  is  a  simple  form  of  generator  whose  stationary  armature  con- 
sists of  a  permanent  magnet,  more  or  less  horseshoe-  or  U-shaped, 
upon  which  is  wound  a  single  coil  of  insulated  wire. 

The  gap  between  the  ends  of  the  magnet  is  alternately  bridged 
by  a  keeper  and  opened  by  its  removal.  The  nature  of  its  con- 
struction and  operation  is  illustrated  by  winding  an  insulated 
copper  wire  around  the  bar  of  an  ordinary  horseshoe-  or  U- 
shaped  magnet  and  electrically  connecting  the  ends  of  the  wire 
so  as  to  form  a  closed  coil.  When  the  keeper  is  removed  from 
the  magnet  an  electric  current  is  induced  in  the  coil.  The  same 
is  true  when  the  keeper  is  replaced.  The  quicker  the  removal 
and  replacement  of  the  keeper  the  greater  the  current  generated. 

If  the  magnet  is  of  sufficient  size  and  strength,  and  the  move- 
ment of  the  keeper  is  rapid,  an  arc  can  be  drawn  by  separating 
the  ends  of  the  wire  at  the  same  instant  that  the  keeper  is  removed 
or  replaced.  It  is  not  necessary  that  the  keeper  shall  come  into 
metallic  contact  with  the  magnet  poles.  The  same  effect  can  be 
produced  by  passing  a  bar  of  iron  or  soft  steel  between  the  poles 
of  the  magnet. 

One  form  of  apparatus  used  for  ignition  by  a  current  generated 
in  this  manner  has  an  air  gap  in  the  magnet  core  nearly  closed 


IGNITION  77 

most  of  the  time  by  the  edge  of  a  rotating  iron  'disk  or  the  rim 
of  a  wheel  that  passes  between  the  poles.  The  disk  or  wheel  is 
attached  to  the  crank  shaft  of  the  motor.  A  notch  is  cut  in  the 
disk  edge  or  wheel  rim.  As  the  notch  passes  between  the  magnet 
poles  the  magnetic  circuit  is  interrupted,  as  by  removing  the 
keeper  from  the  poles,  and  a  current  is  induced  in  the  coils.  The 
contact  points  are  separated  at  the  same  instant  in  the  combustion 
chamber  and  an  arc  is  drawn.  The  contact  points  and  the  induc- 
tion coil  are,  of  course,  electrically  connected. 

The  notch  in  the  disk  or  wheel  rim  is  generally  filled  with  some 
non-magnetic  material,  such  as  copper,  brass,  lead,  wood,  wood 
fiber,  etc.,  so  as  to  form  continuous  smooth  surfaces. 

42.  High-Tension  Jump-Spark  Electric  Ignition  in  General.  — 
A  single  electric  spark,  or  a  series  of  sparks,  jumping  across  a 
permanent  gap  or  break  in  the  metallic  circuit,  and  passing 
through  the  combustible  mixture  in  the  cylinder  of  a  motor,  is 
the  means  adopted  to  a  very  considerable  extent  for  igniting  the 
charge  in  an  internal-combustion  motor.  A  high  electromotive 
force  or  pressure  is  necessary  to  force  the  -park  across  the  gap. 
This  is  secured  by  the  use  of  an  induction  coil  that  transforms 
a  current  of  an  ampere  or  less  and  of  only  a  few  volts  pressure 
into  electric  energy  of  enormously  higher  tension  and  correspond- 
ingly less  volume.  The  low-tension  current  is  supplied  by  a 
battery  or  a  low-tension  generator.  A  "timer"  is  used  in  con- 
nection with  the  battery.  The  function  of  the  timer  is  to  close 
the  battery  circuit  so  that  a  current  can  flow  from  the  battery 
through  the  induction  coil  at  the  proper  instant  to  produce 
a  spark  in  the  combustion  chamber.  A  generator,  instead 
of  the  battery,  is  very  often  used  to  supply  the  low-tension 
current. 

The  generator,  the  timer,  the  induction  coil,  and  a  distributer 
for  directing  the  high-tension  current  to  the  different  combustion 
chambers  of  a  multi-cylinder  motor,  are  all  sometimes  brought 
together  and  embodied  in  a  single  piece  of  apparatus.  This 
combination  is  commonly  known  as  a  high-tension  magneto, 
because  a  magneto  generator  has  been  used  for  this  purpose  up 
to  the  present  time. 


THE   GAS  ENGINE 


43.    Jump-Spark  Igniters  for  Electric  Ignition.    Spark  Plugs. — 

The  jump-spark  igniter  for  high-tension  ignition  is,  with  few 
exceptions,  made  up  of  a  central  metal  wire  surrounded  by  a 
thick  tube  of  insulating  material  which,  in  turn,  fits  into  a  hol- 


FIG.  43. 
Spark  Plug  for  High-Tension  Jump-Spark  Ignition.     Porcelain  Insulation. 

The  central  rod  or  wire  S  is  insulated  from  the  outer  metal  parts  by  the  porce- 
lain P.  Asbestos  packing  is  used  around  the  swell  just  below  the  middle  of 
the  porcelain.  Copper  or  asbestos  packing  is  used  on  the  central  wire  at  the 
shoulder  U.  The  spark  jumps  across  the  gap  between  the  lower  end  of  the 
central  wire  and  the  curved  wire  set  into  the  lower  end  of  the  outer  metallic 
bushing. 

low  metal  plug  threaded  on  the  outside  so  as  to  screw  into  a 
threaded  hole  in  the  wall  of  the  cylinder  of  the  motor  or  into 
some  part  that  fits  into  the  cylinder  wall.  The  insulating  material 


IGNITION 


79 


is  generally  either  porcelain  or  mica.  The  former  is  used  in  one 
tubular  piece,  and  the  latter  is  made  up  of  numerous  disks 
perforated  for  the  central  wire  and  placed  side  by  side  over  it. 
Lava  is  also  used  for  insulation  to  a  limited  extent.  When 
porcelain  is  used,  tight  joints  are  made  between  the  central  wire 
and  the  porcelain,  and  between  the  porcelain  and  outer  bush- 
ing, by  the  use  of  asbestos  fiber  packing  or 
of  soft  copper  washers.  A  fine  copper  wire 
wrapped  with  the  asbestos  fiber  is  especially 
convenient  for  this  purpose.  In  general 
practice  either  the  central  wire  of  the 
spark  plug  terminates  in  an  end  of  small 
diameter  near  some  part  of  the  outer  shell, 
or  a  small  wire  is  fastened  to  the  outer  shell 
and  brought  near  the  enlarged  end  of  the 
central  wire.  The  gap  left  between  the  end 
of  the  wire  and  the  larger  body  of  metal 
near  which  the  wire  terminates,  is  jumped 
by  the  spark  when  the  igniter-  is  in  oper- 
ation. This  gap  is  called  the  "  spark 
Its  width  is  about  one-thirty-second 


gap. 


FIG.  44. 

Spark  Plug  for  Jump 
Spark, 
lation. 


Mica  Insu- 


ers  of  sheet  mica. 
The  black  portion 
indicates  the  mica. 


of  an  inch.  The  insulation  between  the 
central  wire  and  the  outer  shell  is  all  the 
insulation  that  is  between  the  two  sides  of 
the  high-tension  circuit  at  the  spark  plug.  The  insulation  is  made 
The  standard  size  of  the  plug  is  that  of  up  of  disks  or  wash- 
a  half-inch  gas-pipe  plug  as  made  in  this 
country.  The  French  plug  is  smaller  at  the 
threaded  part  of  the  outer  shell,  but  of  nearly 
the  same  size  elsewhere.  Plugs  intended  for  special  motors 
are  generally  larger  than  the  American  standard.  One  special 
type  has  two  insulated  wires  passing  through  a  plate  of  con- 
siderable diameter.  This  secures  double  insulation  between 
the  two  sides  of  the  high-tension  circuit.  The  ends  of  the 
wires  are  brought  to  within  about  one-thirty-second  of  an  inch 
of  each  other.  This  type  of  plug  is  held  in  place  by  a  yoke 
that  spans  it. 


80  THE   GAS  ENGINE 

44.  Timers  for  High-Tension  Electric  Ignition.  —  When  a 
battery  is  used  to  supply  current  for  high-tension  jump-spark 
ignition,  a  timer  is  placed  in  the  battery  circuit  to  close  it  at  the 
moment  a  spark  is  required.  The  timer  controls  the  time  of 
flow  of  the  low-tension  current.  Of  the  principal  parts  of  the 
timer,  one  is  stationary  and  the  other  rotates.  They  are  elec- 
trically insulated  from  each  other.  As  the  rotor  revolves,  a  metal 
contact  piece  on  it  comes  against  the  metal  of  the  stationary  part 
at  intervals  and  closes  the  electric  circuit.  There  are  as  many 
metallic  contact  pieces  on  the  stationary  part  as  there  are  induc- 
tion coils  in  use  for  operating  the  motor,  in  the  more  common 
and  simpler  device.  (Other  forms  will  be  described  later.) 
The  contact  pieces  are  placed  around  the  circular  path  of  the 
rotating  contact  piece  so  as  to  close  the  circuit  at  the  time  re- 
quired for  each  cylinder  of  the  motor.  The  stationary  part  is 
adjustable  to  a  slight  extent  by  rotary  motion  around  the  rotor 
shaft,  so  that  the  time  of  closing  the  circuit  can  be  varied  to  meet 
the  requirements  of  the  motor. 

In  the  better  modern  designs  the  stationary  part  generally 
consists  of  a  ring  of  wood  fiber  supported  on  a  metal  part 
that  is  bored  to  receive  the  shaft  of  the  rotor.  The  contact 
points  in  the  stationary  part  are  attached  to  the  insulating  ring 
so  as  to  be  insulated  from  each  other  and  from  the  shaft  of 
the  rotor.  The  rotor  has  only  one  contact  piece,  and  in  some 
designs  it  has  rigid  metallic  connection  with  the  rotor  shaft; 
in  others  it  is  insulated  from  the  shaft,  but  permanently  con- 
nected by  a  rubbing  or  rolling  contact  with  the  metal  ring  that 
is  part  of  the  stationary  member  of  the  timer  and  is  electrically 
connected  to  the  metal  of  the  motor.  The  contacts  are  pressed 
together  by  the  action  of  a  spring.  The  moving  parts  are  either 
packed  with  soft  grease  or  copiously  lubricated  with  oil. 

In  automobile  practice  the  frequent  movement  of  the  adjust- 
able (stationary)  part  of  the  timer  breaks  the  wires  that  lead 
from  its  contact  pieces  to  the  other  parts  of  the  apparatus.  In 
order  to  prevent  this  trouble  the  adjustable  part  is  surrounded 
by  a  case  that  is  truly  stationary  with  regard  to  the  -motor  frame, 
and  the  leading-out  wires  are  connected  to  binding  posts  on  the 


IGNITION  8 1 

casing.  The  electrical  connections  between  tfye  case  and  the 
adjustable  part  are  made  by  sliding  contact. 

The  speed  of  rotation  of  the  timer  is  half  that  of  the  crank 
shaft  in  the  ordinary  type  of  four-cycle  motor.  In  the  two- 
cycle  motor  the  timer  rotates  at  the  same  speed  as  the  crank 
shaft. 

45.  Induction  Coils  for  Electric  Ignition.  —  The  induction 
coil  used  for  high-tension  ignition  in  motor  practice  has  a  central 
core  of  very  soft,  small  iron  wires  arranged  in  a  circular  bundle. 
Insulating  material  in  the  form  of  a  tube  covers  the  core.  Com- 
paratively coarse  copper  wire  is  wound  around  the  insulating 
tube  in  the  form  of  a  solenoid  coil  of  a  few  layers  and  several 
turns.  This  is  the  low-tension  coil,  primary  coil,  or  battery  coil. 
The  turns  of  wire  are  insulated  from  each  other  either  by  using 
a  wire  with  an  insulating  covering  or  by  carefully  winding  bare 
wire  over  a  thickness  of  sheet  insulation  for  each  layer,  so  that 
the  turns  of  wire  do  not  touch  each  other,  and  then  filling  the 
spaces  between  the  wires  with  paraffine.  One  end  of  the  pri- 
mary-coil wire  is  attached  to  a  binding  post  for  receiving  a  battery 
wire,  and  the  other  end  connects  to  a  device  for  interrupting  the 
current. 

The  interrupter  has  a  thin,  flat  spring  (vibrator,  trembler) 
that  is  rigidly  held  at  one  end  so  that  a  metal  contact  point  near 
the  free  end  is  pressed  against  a  mating  point.  The  metal 
parts  to  which  the  two  contact  points  are  attached  are  electri- 
cally insulated  from  each  other  when  the  points  are  separated. 
The  second  wire  from  the  battery  is  connected  to  the  part  of  the 
interrupter  that  is  insulated  from  the  side  to  which  the  primary- 
coil  wire  is  connected.  The  free  end  of  the  spring  has  attached 
to  it  a  disk  of  soft  iron  that  is  held  just  opposite  one  end  of  the 
soft-iron  core  of  the  coil  and  at  a  short  distance  from  it.  When 
a  current  of  electricity  is  passed  through  the  coil  it  magnetizes 
the  iron  core,  which  then  attracts  the  metal  disk  and  draws  both 
it  and  the  free  end  of  the  spring  toward  it.  The  contact  points 
are  thus  separated  and  the  current  interrupted.  The  core  then 
quickly  loses  its  magnetism,  and  the  elasticity  of  the  spring 
brings  the  contact  points  together,  so  that  current  again  passes 


82  THE   GAS  ENGINE 

through  the  coil.  This  operation  is  repeated  and  continued  as 
long  'as  the  battery  supplies  sufficient  current. 

A  second  coil  (secondary  coil,  high-tension  coil,  spark-plug 
coil)  is  wound  over  the  first.  It  is  of  exceedingly  thin  wire  and 
has  an  extremely  great  number  of  turns.  The  turns  and  layers 
of  wire  are  insulated  from  each  other  in  the  same  manner  as  in 
the  inner  coil.  The  outer  coil  is  carefully  insulated  from  the 
inner  one  that  carries  the  low-tension  battery  current.  One 
end  of  the  outer  coil  is  connected  to  the  same  binding  post  as 
the  end  of  the  inner  coil  of  coarse  wire  (primary  coil).  The 
other  end  of  the  outer  coil  is  terminated  at  a  binding  post  of  its 
own.  The  apparatus  thus  has  three  binding  posts  or  terminals 
for  receiving  wires  from  outside. 

One  terminal  is  at  the  battery  side  of  the  interrupter;  an- 
other, which  may  be  called  the  intermediate  terminal,  is  between 
the  ends  of  the  inner  and  outer  coils;  and  the  third  terminal  is 
at  the  remaining  end  of  the  outer  coil. 

The  inner  coil  of  coarse  wire  and  few  turns  is  designated,  as 
has  already  been  indicated,  either  as  the  primary  winding  or 
coil,  the  low-tension  winding  or  coil,  or  the  battery  winding  or 
coil. 

The  outer  coil  of  thin  wire  and  many  turns  is  known  as  the 
secondary  winding  or  coil  or  as  the  high-tension  winding  or  coil. 

When  the  battery  current  stops  flowing  through  the  primary 
winding  it  induces  a  current  of  extremely  high  pressure  and 
very  small  volume,  or  amperage,  in  the  secondary  winding. 
For  ignition  purposes  the  tension  of  this  secondary  current 
should  be  at  least  great  enough  to  give  a  spark  across  a  one- 
quarter-inch  air  gap. 

An  electric  condenser  is  used  in  connection  with  the  parts  of 
the  induction  coil  that  have  just  been  described,  and  is  a  com- 
ponent part  of  the  apparatus.  Its  function  is  to  strengthen  the 
action  of  the  coil  and  protect  the  contact  points  at  the  interrupter 
from  fusing.  The  condenser  is  made  up  of  sheets  of  tin  foil 
and  paraffined  paper  laid  together  alternately,  so  that  the  paper 
insulates  the  sheets  of  foil  from  each  other.  Alternate  sheets  of 
the  foil  are  connected  together  electrically  to  form  one  pole  of 


IGNITION  83 

the  condenser,  and  the  remaining  sheets  are  likewise  connected 
together  to  form  the  other  pole  of  the  condenser.  One  pole  of 
the  condenser  is  connected  to  the  battery  side  of  the  interrupter, 
and  the  other  pole  to  the  primary-coil  side. 

When  the  contact  points  of  the  interrupter  are  separated  there 
is  a  tendency  for  the  battery  current  to  keep  flowing  in  an  arc 
across  the  gap  thus  formed.  The  magnetic  core,  acting  induc- 
tively on  the  primary  coil,  also  has  a  tendency  to  maintain  the 
arc. 

The  condenser  counteracts  this  combined  effort  to  maintain 
an  arc  at  the  interrupter  contacts,  by  receiving  and  storing  the 
electric  energy  and  thus  breaking  down  the  arc  quickly.  The 
energy  stored  in  the  condenser  is  probably  discharged  back 
through  the  primary  circuit  immediately  after  the  primary 
current  is  stopped,  thus  further  increasing  the  inductive  action 
and  the  strength  of  the  spark. 

The  induction  coil,  when  not  constructed  especially  for  ignition 
purposes,  usually  has  four  terminals  instead  of  three.  Each 
end  of  the  two  coils  is  provided  with  its  own  binding  post.  Such 
coils  are  still  used,  to  a  limited  extent,  for  ignition  purposes. 

All  parts  of  the  induction-coil  apparatus,  except  the  inter- 
rupter and  binding  posts,  are  enclosed  in  a  box  or  case  and 
surrounded  with  paraffine  poured  in  while  melted. 

American  induction  coils  for  ignition  purposes  are  generally 
wound  to  operate  on  from  six  to  seven  volts.  Most  of  the  foreign 
coils  require  only  about  four  volts. 

A  voltage  much  higher  than  that  for  which  the  induction  coil 
is  constructed  should  not  be  applied  to  the  primary  coil.  It  will 
injure  the  contact  points  by  fusing  and  oxidizing  them,  and  if 
very  much  in  excess  of  the  right  amount,  may  destroy  the  coil  by 
breaking  down  the  insulation  in  the  winding. 

46.  Batteries  for  Electric  Ignition.  —  Storage  batteries  and 
those  made  up  of  dry  primary  cells  are  the  only  kinds  used  for 
ignition  to  any  extent  on  automobiles  and  launches.  They  are 
the  most  suitable  for  the  same  use  in  connection  with  stationary 
motors,  even  though  the  spilling  of  the  liquid  of  a  wet  cell  does 
not  have  to  be  considered.  The  high  internal  resistance  and  the 


84  THE  GAS  ENGINE 

polarization  of  wet  primary  cells  when  in  use    are    the  main 
obstacles  to  their  adoption  for  stationary  motors. 

47.  Dry  Batteries.  —  The  primary  dry  cell  that  finds  most 
use  for  ignition,  has  zinc  and  carbon  for  its  elements;  the  electro- 
lyte is  a  solution  of  sal  ammoniac  in  water. 

The  sheet  zinc  used  is  made  up  into  a  round,  cylindrical,  open- 
top  cell.  A  solid  stick  of  carbon  (coke)  is  placed  in  the  middle 
of  the  cell  and  packed  in  with  rather  finely  granulated  coke. 
Absorbent  paper,  such  as  blotting  paper,  is  placed  at  the  bottom 
and  top  of  the  cell.  The  granulated  coke  is  saturated  with  the 
sal-ammoniac  solution.  The  top  of  the  cell  is  sealed  with  a  thick 
layer  of  pitch,  poured  in  hot,  and  the  end  of  the  carbon  stick 
protrudes  through  the  pitch  cap.  A  binding  post  is  attached  to 
the  carbon  and  another  to  the  edge  of  the  sheet  zinc. 

The  electromotive  force  of  a  carbon-zinc-sal  ammoniac  dry 
cell  is  about  ij  volts  when  the  cell  is  not  giving  out  current. 
The  voltage  drops  while  it  is  delivering  current.  From  i  to  ij 
volts  is  as  much  as  a  dry  cell  will  ordinarily  maintain  when 
furnishing  electricity  to  an  induction  coil  used  for  ignition,  even 
while  the  cell  is  still  in  good  condition.  Dry  cells  run  down 
rapidly  in  both  voltage  and  capacity  when  in  use  for  ignition,  and 
some  even  deteriorate  rapidly  while  still  new  and  not  in  use. 

The  carbon  is  called  the  positive  element  of  the  dry  cell  just 
described,  and  the  zinc  is  called  the  negative  element.  They  are 
indicated  by  the  signs 


(+ )  for  the  positive  element; 
( —  )  for  the  negative  element. 


48.  Series  and  Multiple  Batteries.  —  When  dry  cells  are  used 
for  ignition  they  must  be  connected  together  in  groups  so  as  to 
give  the  required  pressure  and  current. 

For  convenience  the  words  carbon  and  zinc  will  often  be  used 
instead  of  positive  and  negative,  in  referring  to  the  various  battery 
connections. 

In  series  battery  connection  the  carbon  of  one  cell  is  elec- 
trically connected  to  the  zinc  of  another,  from  cdl  to  cell.  A 
positive  element  is  left  free  at  one  end  of  the  series  of  cells,  and 


IGNITION  85 

likewise  a  negative  element  at  the  other  end.     These  two  free 
elements  are  the  terminals  of  the  battery. 

The  connection  of  cells  in  series  has  the  effect  of  adding  their 
voltages  together  to  produce  a  voltage  equal  to  their  sum.  If  all 
the  cells  have  the  same  voltage,  then  the  voltage  obtained  by 
connecting  them  in  series  is  found  by  multiplying  the  voltage  of 

Carbon  Terminal 
of  Batterys 

i  Zinc  Terminal 
of  Battery 


FIG.  45. 

Battery  of  Four  Series-Connected  Cells, 
ij  volts  per  cell.     5  volts  between  (+)  and  (— ). 

one  cell  by  the  number  that  are  connected  in  series.  If  five  cells 
whose  working  pressure  (when  delivering  current)  is  ij  volts 
each,  are  connected  in  series,  the  voltage  between  the  terminals 
of  the  battery  will  be  $  X  i%  =  61  volts.  This  is  about  the 
voltage  for  American  induction  coils  for  high-tension  ignition 
purposes. 

The  voltage,  or  electromotive  force,  of  a  battery  is  the  measure 
of  the  pressure  that  forces  electric  current  through  the  circuit  to 
be  traversed.  All  parts  of  the  circuit,  including  the  battery 
itself,  offer  resistance  to  the  flow  of  current.  The  current  must 
pass  through  the  battery,  therefore  the  internal  resistance  of  the 
battery  must  be  added  to  the  resistance  of  the  external  circuit 
(external  resistance)  in  order  to  obtain  the  value  of  the  total 
resistance.  The  amount  of  current  that  a  given  voltage  will 
send  through  a  given  circuit  is  inversely  proportional  to  the  total 
resistance  of  the  circuit. 

The  elementary  equation  representing  this  is 

Electromotive  force 


Current  = 


Total  resistance  of  circuit 

Electromotive  force 

Internal  resistance  +  external  resistance 


86  THE   GAS  ENGINE 

If  the  external  resistance  of  the  circuit  is  so  great  in  comparison 
with  the  internal  resistance  of  the  battery  as  to  make  the  latter 
insignificant  in  comparison,  then  the  current  that  a  battery  will 
give  is  almost  exactly  proportional  to  the  number  of  series- 
connected  cells  of  equal  voltage  in  the  battery.  But,  on  the 
other  hand,  if  the  external  resistance  of  the  circuit  is  very  small 
in  comparison  with  the  internal  resistance  of  the  battery,  as  when 
the  terminals  of  the  battery  are  connected  by  a  thick,  short 
copper  wire,  the  addition  of  cells  of  equal  voltage  and  internal 
resistance,  connected  in  series,  will  not  appreciably  affect  the 
amount  of  current  that  will  flow,  for  the  total  resistance  of  the 
circuit  is  increased  in  nearly  the  same  proportion  as  the  electro- 
motive force. 

Increasing  the  number  of  cells  in  a  series-connected  battery 
does  not  increase  the  current  in  the  same  proportion.  But  when 
the  circuit  includes  an  operating  induction  coil  the  proportionate 
increase  of  current  is  greater,  and  more  nearly  in  proportion  to 
the  number  of  cells,  than  is  indicated  by  an  equation  dealing  only 
with  current,  electromotive  force,  and  resistance  when  the  latter 
is  measured  by  a  continuous,  uniform  flow  of  current.  The 
reason  for  this  is  that  the  inductive  resistance  of  the  circuit  on 
account  of  the  rapid  change  in  the  rate  of  flow  of  current  as  the 
.interrupter  works  greatly  increases  the  external  resistance  above 
that  which  the  external  resistance  offers  to  a  steady  flow  of 
current. 

Under  the  usual  conditions  of  high-tension  battery  ignition, 
increasing  the  number  of  cells  in  a  series-connected  battery  very 
materially  increases  the  current  that  flows  through  the  primary 
winding  of  the  induction  coil.  The  volume  or  hotness  of  the 
spark  is  also  very  materially  increased  as  long  as  the  magnetic 
core  of  the  induction  coil  is  not  nearly  or  completely  saturated. 
(Saturated  =  magnetized  to  its  full  capacity.) 

In  multiple  battery  connection  all  the  carbons  are  connected 
together,  as  by  a  single  wire,  and  all  the  zincs  are  similarly  con- 
nected together.  The  two  wires  are  the  terminals  of  the  battery. 
The  voltage  of  the  battery  is  the  same  as  that  of  a  single  cell, 
when  all  the  cells  are  of  equal  electromotive  force.  The  current 


IGNITION 


that  the  battery  will  give  is  but  slightly  more  than  that  of  a  single 
cell  when  the  external  resistance  is  very  high  in  proportion  to  the 
internal  resistance  of  a  cell.  But  when  the  resistance  of  the  exter- 
nal circuit  is  very  small  in  comparison  with  that  of  a  cell,  the 
current  will  be  nearly  proportional  to  the  number  of  cells. 


— )  Terminal 


minal 


FIG.  46. 

Battery  of  Multiple  or  Parallel-Connected  Cells. 
i£  volts  per  cell;  also  ij  volts  between  (-}-)  and  (— ). 

The  facts  just  pointed  out  goto  show  that  if  one  cell  is  sending  an 
electric  current  through  a  circuit,  and  it  is  desired  to  increase  the 
current  to  the  greatest  value  possible  by  the  addition  of  another 
cell,  they  should  be  connected  in  series  (carbon  to  zinc)  if  the 
external  resistance  of  the  circuit  is  large;  but  if  it  is  small,  they 
should  be  connected  in  multiple  (zinc  to  zinc  and  carbon  to  car- 
bon). The  inductive  resistance  is  to  be  included  in  the  external 
resistance  of  the  circuit.  It  is  assumed  that  the  cells  are  exactly 
alike. 


FIG.  47. 

Two  Sets  of  Four  Series-Connected  Cells  in  Multiple  or  Parallel, 
ij  volts  per  cell.     5  volts  between  (+)  and  (— ). 

49.  Multiple-Series  Batteries.  —  A  group  of  series-connected 
cells  can  be  considered  as  one  of  the  units  of  which  a  battery  is 
made  up.  In  determining  the  pressure  and  current  capacity  of  a 


88 


THE   GAS  ENGINE 


battery  of  such  units,  the  work  may  be  facilitated  by  imagining 
each  series-connected  group  to  be  a  single  cell  whose  carbon  and 
zinc  correspond  to  the  terminals  of  the  group.  The  electro- 
motive force  of  this  imaginary  cell  is  the  same  as  that  of  the  series. 
The  effects  on  pressure  and  current  obtained  by  connecting  these 
groups  either  in  series  or  multiple  are  similar  to  those  already 
pointed  out  for  series  and  multiple  arrangement  of  single  cells. 

Thus,  if  five  cells  connected  in  series  is  the  unit,  whose  electro- 
motive force  is  6^  volts,  then  putting  two  of  these  units  in  series 
with  each  other  will  give  2  X  6J  =  12 J  volts;  or  putting  the  two 
units  in  multiple  will  leave  the  pressure  6J  volts  as  before.  And 
as  for  single  cells,  any  number  of  the  series-connected  units 
when  connected  in  multiple  do  not  increase  the  pressure. 

50.  Arrangement  of  Batteries  for  Ignition.  —  It  is  advisable 
to  have  the  batteries  in  duplicate  for  ignition  purposes.  Only 
one  battery  is  used  at  a  time.  This  leaves  a  reserve  to  be  called 
on  in  case  the  one  in  use  at  the  moment  fails.  If  both  batteries 


Switch  Open 


FIG.  48. 

Incorrect  Wiring  for  Two  Batteries  in  Parallel. 

Current  flows  as  indicated  by  the  arrows  when  the  switch  is  open  and  exhausts  the 
upper  row  of  six  cells.  Current  also  flows  in  the  same  manner  when  the  circuit 
is  not  closed  by  the  timer  of  the  ignition  system. 

become  too  weak  to  supply  enough  current  when  either  is  used 
alone,  they  can  both  be  used  together.  Simple  and  inexpensive 
switches  for  throwing  either  one  or  both  batteries  on  are  found 
in  numerous  designs.  Such  switches  connect  the  two  batteries 


IGNITION 


89 


in  multiple  when  both  are  used  at  the  same  instant.  The  two 
batteries  when  thus  connected  really  form  a  single  multiple-series 
battery. 

In  jump-spark  electric  ignition  for  motors  the  resistance  of 
the  circuit  that  is  external  to  the  battery  is  generally  of  such  an 
amount  that  the  following  method  of  arranging  the  cells  can  be 
used  to  advantage  when  there  are  originally  two  batteries. 

After  both  batteries  have  become  too  weak  to  give  sufficient 
current  when  used  individually,  they  can  first  be  connected  in 
multiple,  as  already  described,  and  used  until  still  further  weak- 
ened to  such  an  extent  as  to  fail  to  supply  the  necessary  energy. 


Induction  Coil 


Switch  Open 


FIG.  49. 
Correct  Wiring  for  Two  Batteries  in  Parallel. 

No  current  flows  when  the  switch  is  open.     The  switch  when  in  mid-position  puts 
the  two  batteries  in  parallel. 

The  two  original  batteries  can  then  be  connected  in  series  and 
they  will  then  generally  give  enough  current  for  a  while.  Some- 
times it  is  advisable  not  to  change  directly  from  multiple  to  series 
connection  of  all  the  cells,  but  instead  to  put  only  part  of  the 
cells  of  one  battery  in  series  with  all  those  of  the  other  and 
then  add  the  remaining  cells  in  series  as  they  are  needed. 

When  dry  cells  are  used  for  low-tension  arc  ignition  a  gain  of 
current  can  be  obtained  by  putting  two  batteries  in  multiple 
after  they  have  each  run  down  so  that  neither  alone  will  give 
enough  current.  There  is  no  further  gain  by  putting  them  in 


90  THE   GAS  ENGINE 

series,  however,  when  the  external  resistance  of  the  circuit  is  as 
low  as  in  the  usual  practice  for  arc  ignition. 

51.  Recuperation  of  Dry  Cells.  —  Most  carbon-zinc  dry  cells 
can  be  temporarily  recuperated  by  making  a  hole  in  each  and 
putting  in  a  solution  of  sal  ammoniac  in  water,  or  by  putting  in 
water  alone.     The  rejuvenation  thus  secured  is  generally  of  short 
duration,  however. 

52.  Storage  Batteries,  also  called  Accumulators  and  Second- 
ary Batteries.  —  The  storage  battery  for  ignition   purposes   is 
ordinarily  made  up  of  two  or  three  storage  cells,   all  placed 
together  in  a  single  case,  or  in  a  large  cell,  so  that  the  battery  is 
a  compact  and  inseparable  unit  in  itself,  which  in  many  designs 
has  but  two  external  binding  posts  or   terminals.     In    others 
the  terminals  of  each  cell  are  brought  outside  of  the  case  and 
connected  together  to  form  the  battery.     Two  of  the  cell  termi- 
nals are  left  free,  of  course,  to  form  the  battery  terminals. 

The  storage  cells  are  made  up  of  positive  and  negative  plates. 
In  one  type  the  plates  are  of  lead  with  numerous  perforations 
or  pockets  which  are  filled  with  oxide  of  lead  in  the  form  of 
paste.  Several  of  these  plates,  or  grids,  are  connected  to  form 
the  positive  side  of  the  cell,  and  another  set  for  the  negative 
side.  The  positive  and  negative  grids  are  interposed  between 
each  other,  and  the  intervening  spaces  are  filled  with  a  liquid 
electrolyte  of  dilute  sulphuric  acid. 

When  first  made  up  the  cell  has  no  electric  life,  but  must  be 
charged  by  passing  a  current  of  electricity  through  it.  When 
charged,  the  terminal  of  one  set  of  plates  becomes  electro- 
positive and  that  of  the  other  set  electro-negative.  When  the 
cells  are  recharged,  it  must  always  be  done  so  that  each  set  of 
plates  retains  its  initial  polarity.  The  terminals  of  the  battery 
are  therefore  marked  in  some  manner  to  indicate  which  is  posi- 
tive and  which  negative.  In  ignition  storage  batteries  the 
terminals  are  usually  marked  (+)  and  (— )  to  indicate  positive 
and  negative  respectively. 

The  charging  of  the  storage  battery  can  be  done  from  any 
source  that  will  furnish  direct  current  (not  alternating)  of  suffi- 
cient pressure.  The  pressure  of  the  charging  current  must  be 


IGNITION  91 

higher  than  that  of  the  battery  when  it  is  fully§  charged.  The 
current  must  not  be  allowed  to  exceed  a  certain  maximum  am- 
perage that  depends  on  the  area  of  the  surface  of  the  grids. 
There  are  generally  instructions  with  the  battery  which  give 
the  maximum  allowable  current  for  charging.  The  charging 
process  is  one  of  chemical  change  in  the  lead  oxide.  If  done 
too  rapidly,  gases  are  formed  too  rapidly  and  the  paste  loosened 
in  the  pockets. 

Before  connecting  the  charging  wires  to  the  terminals  of  the 
battery,  it  is  necessary  to  know  which  of  the  wires  is  positive 
and  which  negative,  so  that  they  can  be  connected  accordingly. 
A  very  simple  and  convenient  method  of  determining  the  polarity 
of  the  charging  wires  is  to  immerse  their  ends  in  water.  Bubbles 
of  gas  will  form  on  the  immersed  surface  of  the  negative  (— ) 
wire  more  rapidly  than  on  the  positive  (+  ).  The  wire  on  which 
the  greater  formation  of  bubbles  occurs  should  be  connected  to 
the  negative  terminal  of  the  storage  battery,  and  the  other  wire 
to  the  positive  terminal  of  the  battery. 

In  testing  for  the  positive  and  negative  wires  it  is  advisable 
to  keep  their  ends  well  apart  when  they  are  first  immersed  in  the 
water,  and  then  bring  them  toward  each  other  gradually  till  the 
bubbles  show  distinctly.  An  excessive  flow  of  current  will  thus 
be  prevented  in  cases  where  it  would  occur  with  the  wire  ends 
close  together.  Impure  or  slightly  acidulated  water  will  give 
bubbles  more  readily  than  pure  water,  on  account  of  the  lower 
electrical  resistance  of  the  former.  In  case  the  memory  fails 
as  to  the  pole  at  which  the  bubbles  form  most  rapidly,  wires  can 
also  be  connected  to  the  terminals  of  the  storage  battery  to  be 
charged  and  their  free  ends  immersed  in  water.  The  formation 
of  bubbles  should  be  noted  as  for  the  charging  wires.  The 
two  wire  ends  that  give  most  bubbles  in  the  two  cases  should  be 
connected  together  for  charging.  Acidulated  water  is  generally 
required  to  bring  out  the  bubbles  with  the  voltage  of  the  ignition 
storage  battery. 

The  case  enclosing  the  ignition  storage  battery  is  tightly  closed 
when  the  battery  is  in  use.  But  when  charging,  each  cell  is 
opened  to  the  atmosphere  by  the  removal  of  a  stopper  to  a  hole 


92  THE   GAS  ENGINE 

in  the  cell,  or  by  other  means.  This  is  necessary  to  allow  the  gas 
slowly  formed  during  charging  to  escape.  When  the  battery  is 
completely  charged,  the  formation  of  the  gases  by  the  continu- 
ance of  the  charging  current  is  much  more  rapid  than  before. 
Charging  should  be  discontinued  as  soon  as  gases  begin  to  form 
rapidly. 

Rectifiers  for  transforming  alternating  current  into  direct 
current  are  used  for  charging  storage  batteries  when  the  source 
of  electrical  supply  has  an  alternating  current. 

The  electromotive  force  of  the  lead-grid  storage  cell  is  brought 
up  to  about  2.5  volts  while  charging.  It  quickly  drops  a  tenth 
of  a  volt  or  so  when  it  begins  to  discharge.  When  it  has  fallen 
to  2.1  volts  per  cell  the  battery  should  not  be  used  till  charged 
again.  Three  cells  in  series,  giving  an  average  of  about  6.5 
volts,  are  put  together  for  the  battery  to  be  used  in  connection 
with  American  induction  coils,  according  to  the  usual  practice. 

Storage  cells  with  other  elements  than  lead  and  its  compounds 
are  also  in  use  for  ignition  purposes.  In  one,  nickel  and  iron  are 
the  metals  used  for  the  elements.  Another,  a  foreign  production, 
is  really  a  combination  of  a  storage  cell  and  a  primary  cell.  It  is 
charged  by  passing  a  current  through  it  in  the  usual  manner  for 
a  storage  cell.  But  in  order  to  obtain  current  from  it  a  piece  of 
metal,  or  alloy,  is  dropped  into  it.  Current  is  then  given  out 
as  in  the  ordinary  case  of  a  storage  cell.  This  continues  as  long 
as  any  of  the  piece  of  metal  dropped  in  remains.  But  as  soon  as 
the  metal  is  consumed  the  cell  becomes  dead  till  more  metal  is 
dropped  in.  This  makes  it  active  again  as  long  as  the  metal 
lasts.  The  number  of  pieces  of  metal  that  have  been  used  in  a 
battery  after  it  has  been  fully  charged  is  an  index  of  its  degree 
of  discharge.  The  pieces  of  metal  to  be  dropped  in  are  made  of 
uniform  size.  When  a  certain  number  have  been  used  the  cell 
must  be  recharged. 

The  electrical  resistance  of  storage  cells  for  ignition  is  much 
lower  than  that  of  dry  cells,  but  not  so  low  as  that  of  the  larger 
storage  cells  intended  for  power  and  lighting  purposes  where  a 
vastly  larger  current  is  required.  The  ignition  storage  battery 
is,  therefore,  not  so  seriously  injured  by  short-circuiting  as  are 


IGNITION  93 

the  larger  ones,  but  is  exhausted  with  great  rapfidity  when  the 
terminals  are  connected  through  a  circuit  of  very  low  resistance. 

53.  Comparison  of  Dry  Cells  and  Storage  Batteries  for  Ignition 
Purposes.  —  The  storage  battery  has  a  greater  capacity  than  a 
battery  of  dry  cells  of  equal  bulk.     It  also  provides  a  more 
uniform  voltage.     On  account  of  these  properties  it  is  far  more 
desirable  than  dry  cells.     The  two  features  not  so  desirable  are 
the  necessity  of  recharging  and  the  comparatively  high  cost  of  the 
storage  battery.     When  used  in  connection  with  a  generator  that 
supplies  it  with  current  while  both  are  connected  in  the  working 
position  with  the  motor,  the  objection  to  the  necessity  of  recharg- 
ing disappears. 

Many  makes  of  dry  cells  are  notably  unreliable  in  action. 
They  sometimes  have  practically  no  energy  in  them  when  first 
put  in  place.  This  deficiency  may  be  due  either  to  an  originally 
poor  cell  or  to  one  that  has  been  kept  too  long  before  putting  it 
into  use.  It  is  believed  that  nothing  more  than  care  in  selecting 
materials  and  in  construction  is  necessary  to  produce  a  good, 
durable  dry  cell.  When  carelessly  packed,  the  terminals  of  two 
cells  may  come  together  so  as  to  make  a  short  circuit  and  exhaust 
them  both. 

54.  Testing  Electric  Batteries.  —  The  test  for  the  condition 
of  a  storage  battery  with  regard  to  its  capacity  to  deliver  current 
is  made  by  measuring  the  voltage.     It  will  be  remembered  that 
the  voltage  drops  as  the  battery  is  discharged.     Since  the  drop  is 
slight  from  the  highest  to  the  lowest  working  limits,  a  voltmeter 
reading  to  small  fractions  of  a  volt   (milli-voltmeter)  between 
these  limits  is  necessary.     A  storage  battery  may  be  very  much 
out  of  repair  and  still  show  a  satisfactory  pressure.     In  some 
cases  of  this  kind  a  test  of  the  current  will  disclose  that  it  is 
faulty.     The  test  for  current   can  be  made  with  an  ammeter 
in  a  circuit  that  has  from  terminal  to  terminal  of  the  battery 
about  the  same  resistance  as  that  on  which  the  latter  is  intended 
to  work.     This  is  readily  done  by  cutting  the  ammeter  into  the 
regular  circuit.     The  current  will  decrease  rapidly  if  the  bat- 
tery is  seriously  faulty. 

The  ammeter  is  sometimes  applied  directly  to  the  terminals  of 


94  THE   GAS  ENGINE 

the  battery.  This,  if  done  at  all,  should  be  for  only  a  small 
fraction  of  a  second.  The  ammeter  has  a  very  low  resistance, 
and  applying  it  to  the  terminals  without  any  other  resistance  in 
the  circuit  practically  amounts  to  short-circuiting  the  battery. 
The  only  method  of  doing  this  that  is  at  all  safe  for  the  battery 
is  to  connect  one  terminal  of  the  ammeter  to  a  terminal  of  the 
battery  and  then  strike  the  other  battery  terminal  a  glancing 
blow  with  the  free  ammeter  terminal.  The  kick  of  the  ammeter 
needle  is  to  be  observed.  The  circuit  should  not  be  closed  long 
enough  for  even  a  dead-beat  needle  to  come  to  rest.  This  does 
not  refer  to  storage  batteries  other  than  those  constructed  for 
ignition  purposes. 

Dry  cells  and  dry  batteries  can  be  tested  in  the  same  man- 
ner as  that  just  given  for  storage  cells.  The  dry  cell  will  not 
generally  be  so  much  injured  by  short-circuiting  through  the 
ammeter  as  the  storage  cell,  but  still  it  is  never  advisable  to 
hold  the  instrument  in  contact  with  the  terminals  more  than  a 
second  or  two  when  there  is  a  strong  current.  If  the  current 
is  weak,  the  cell  is  poor  and  past  injury  in  this  manner. 
Tests  of  dry  cells  cannot  be  greatly  relied  on,  however,  for  one 
that  shows  full  voltage  and  a  strong  current  after  standing  idle 
will  not  infrequently  fail  in  a  short  time. 

55.  Wiring  Scheme  for  Single-Acting,  Single-Cylinder  Motor 
with  Jump-Spark  Ignition.  —  A  wire  from  one  terminal  of  the 
battery  connects  to  the  induction  coil  at  the  binding  post  that 
forms  part  of,  or  is  directly  connected  to,  one  side  of  the  inter- 
rupter. A  wire  from  the  insulated  stationary  contact  piece  of 
the  timer  is  connected  to  the  induction  coil  at  the  intermediate 
binding  post  where  one  end  of  the  primary  and  one  end  of  the 
secondary  coil  terminate.  The  remaining  terminal  of  the 
battery  is  "grounded"  by  connecting  it  to  the  metal  of  the  motor 
or  any  part  of  the  metal  frame  on  which  the  motor  rests.  If 
the  rotor  of  the  timer  is  electrically  insulated  from  the  shaft  to 
which  it  is  mechanically  attached,  and  thus  from  the  frame  of 
the  motor,  then  a  wire  connects  the  insulated  ground  ring  of 
the  rotor  to  the  metal  of  the  motor  or  its  supporting  frame,  or 
a  slip  ring  and  brush  are  used  for  the  same  or  a  similar  purpose. 


IGNITION 


95 


When  the  timer  rotor  is  not  insulated  from  the  shaft,  no  special 
electric  connection  is  used.  This  completes  the  wiring  of  the 
battery  circuit. 

When  the  timer  closes  the  circuit,  current  passes  from  the 
battery  to  the  interrupter,  then  through  the  primary  winding 
and  on  through  the  timer  to  the  metal  of  the  motor  or  of  the 
frame  that  supports  the  motor,  and  thence  to  the  ground  wire 


Battery 


Spark  Plug — >q — fj 


Cylinder 


Timer  Frame 

FIG.  50. 

Ignition  System  for  Single-Cylinder  Motor.     One  Battery. 
Heavy  black  indicates  frame  or  "ground"  connection. 

of  the  battery  and  through  the  ground  wire  back  to  the  battery 
itself.  A  switch  for  opening  and  closing  the  primary  circuit 
at  will  is  placed  somewhere  in  the  circuit,  generally  between  the 
battery  and  the  induction  coil. 

Only  one  additional  wire  is  required  for  the  high-tension  or 
spark-plug  circuit.  It  connects  the  remaining  terminal  of  the 
induction  coil  to  the  insulated  part  of  the  spark  plug.  The 
high-tension  current  passes  along  this  wire  from  the  induction 
coil  to  the  spark  plug,  jumps  across  the  spark  gap  to  the  metal 
of  the  motor,  and  then  passes  back  to  the  induction  coil  by  way 
of  the  timer  and  the  wire  connecting  the  timer  to  the  terminal 
to  which  an  end  of  each  of  the  windings  of  the  induction  coil  is 
attached. 

It  will  be  seen  from  the  above  that  both  the  primary  and 
secondary  currents  pass  through  the  wire  connecting  the  timer 
to  the  induction  coil.  This  wire  does  not  need  heavy  insulation, 
however,  for  the  high-tension  current  passes  through  it  only 
when  the  circuit  is  closed  by  the  timer,  thus  making  the  potential 


96  THE  GAS  ENGINE 

of  the  wire  practically  the  same  as  that  of  the  motor.  The  insula- 
tion on  the  wire  between  the  timer  and  induction  coil  needs  to 
be  only  sufficient  to  prevent,  when  the  timer  is  not  closed,  the 
primary  current  from  passing  between  the  wire  and  the  motor 
or  parts  electrically  connected  to  the  motor. 

While  the  method  of  wiring  just  given  is  the  best,  no  serious 
injury  is  done  if  the  timer  wire  is  connected  to  the  interrupter 
end  of  the  primary  coil.  With  this  connection,  however,  the 
secondary  current  must  either  jump  the  open  gap  at  the  inter- 
rupter contacts  immediately  after  the  circuit  is  broken  there, 
or  pass  from  the  motor  frame  back  through  the  battery  to  the 
induction  coil.  There  is  "apt  to  be  more  sparking  at  the  inter- 
rupter with  such  connections  than  when  they  are  made  as  first 
given. 

A  properly  constructed  induction  coil  is  not  injured  by  con- 
necting the  battery  wires  to  the  wrong  terminals.  When  there 
is  no  way  of  determining,  by  an  examination  of  the  induction 
coil,  how  the  connections  should  be  made  to  it,  it  can  be  tested 
with  perfect  safety  by  connecting  the  battery  wires  to  it  till  the 
interrupter  vibrates,  provided  the  interrupter  is  so  adjusted  that 
it  will  not  allow  a  large  current  to  flow  through  the  coil  without 
interrupting  it.  The  current  from  a  battery  of  the  right  capacity 
will  do  no  harm  unless  it  is  allowed  to  flow  for  considerable 
time  without  interruption. 

In  testing  for  induction-coil  connections,  the  vibrator  spring 
should  be  set  so  that  it  presses  the  contact  points  together  very 
lightly. 

The  substitution  of  a  low-tension  direct-current  electric  gen- 
erator of  constant  voltage  for  the  battery  does  not  alter  the  wiring 
scheme.  It  is  not  usual,  however,  to  find  an  electric  generator 
used  in  connection  with  a  current  interrupter  on  the  induction 
coil. 

56.  Wiring  Scheme  for  Motor  with  More  than  One  Combustion 
Chamber,  Jump-Spark  Ignition,  and  One  Induction  Coil  for  Each 
Combustion  Chamber.  —  This  differs  from  the  wiring  for  a 
single  combustion  chamber,  as  just  given,  in  the  multiplication 
of  the  spark  plugs,  induction  coils,  number  of  contact  points  on 


IGNITION 


97 


the  timer,  and  the  number  of  wires  connecting  the  induction  coils 
to  the  timer  and  spark  plugs. 

A  wire  is  led  from  one  of  the  battery  terminals  to  one  of  the 
terminals  of  a  switch  at  the  induction  coils,  which  are  grouped 
together,  all  of  them  generally  being  placed  in  one  box.  Each 
induction  coil  is  complete  in  itself,  including  the  interrupter. 

Battery  A 


Switch  open. 

When  the  Switch  is  in  Mid 
Position  the  Batteries  are 
in  Multiple. 


mm 


FIG.  61. 

Ignition  System  for  Four-Cylinder  Motor.     Two  Batteries. 
Heavy  black  indicates  frame  or  "ground"  connection. 

When  the  switch  is  closed,  one  of  the  battery  wires  is  electrically 
connected  to  the  interrupter  ends  of  all  the  induction  coils.  The 
timer  has  as  many  stationary  contact  points  as  there  are  spark 
plugs  to  be  operated.  There  are  as  many  wires  between  the 
timer  and  the  group  of  induction  coils  as  there  are  induction  coils. 
Each  induction  coil  has  its  own  contact  point  at  the  timer,  and  is 


98  THE   GAS  ENGINE 

connected  to  the  latter  by  a  wire  leading  from  the  inter- 
mediate binding  post  of  the  coil.  Each  spark  plug  is  connected 
to  the  remaining  binding  post  of  its  own  induction  coil.  The 
rotor  of  the  timer  and  the  remaining  terminal  of  the  battery 
are  grounded  to  the  metal  of  the  motor  as  for  a  single-cylinder 
motor. 

The  timer,  by  its  rotation,  closes  the  primary  circuit  through 
each  induction  coil  consecutively  in  the  proper  order  and  at  about 
the  instant  the  spark  is  to  pass  in  the  corresponding  combustion 
chamber. 

If  the  explosions  are  to  occur  with  equal  intervals  of  time 
between  them,  then  the  stationary  contacts  of  the  timer  are 
placed  at  equal  distances  apart  around  the  path  traveled  by  the 
rotor's  contact  point.  But  if,  as  is  the  case  of  a  double-acting, 
single-cylinder,  four-cycle  motor,  the  explosions  occur  first  at 
one-half  a  revolution  of  the  crank  shaft  apart,  and  then  not  until 
one  and  a  half  revolutions  more  have  been  made,  then  after 
another  half  revolution,  and  so  on,  the  two  stationary  contacts  of 
the  timer  must  be  placed  at  one-quarter  of  the  circumference 
apart. 

The  low-tension  direct-current  generator  can  be  used  instead 
of  the  battery,  but  its  application  for  this  purpose  is  not 
common. 

57.  Jump-Spark  Ignition  with  High-Tension  Distributer  and 
Battery  Current.  —  In  this  system  of  ignition  the  timer  and 
induction  coils  are  replaced  by  a  single  piece  of  apparatus  com- 
posed of  one  induction  coil,  a  timer,  and  a  distributer  for  directing 
the  high-tension  current  to  the  proper  spark  plug. 

The  timer  closes  the  battery  circuit  through  the  interrupter 
and  the  primary  winding  of  the  coil  whenever  a  spark  is  wanted 
at  any  of  the  spark  plugs.  Since  there  is  only  one  induction  coil, 
a  means  of  directing  the  high-tension  current  to  where  it  is  needed 
becomes  necessary. 

The  distributer  generally  consists  of  an  arm  of  some  sort  that 
is  attached  to  and  rotates  with  the  same  shaft  that  carries  the 
timer  rotor.  As  the  distributer  arm  swings  around  it  comes 
consecutively  opposite  the  terminals  to  which  the  wires  that  lead 


IGNITION  99 

out  to  the  insulated  parts  of  the  different  spark  plugs  are  con- 
nected. The  distributer  has  always  come  opposite  one  of  these 
terminals  when  the  timer  closes  the  primary  circuit. 

In  addition  to  the  spark  gap  in  the  combustion  chamber,  the 
high-tension  current  must  jump  another  small  gap  between  the 
distributer  arm  and  the  terminal  next  to  it. 

By  this  condensing  of  the  apparatus  the  wiring  system  is 
simplified  to  some  extent.  The  wires  necessary  are:  one  wire 
from  the  battery  to  the  induction  coil;  one  from  each  of  the  spark 
plugs  to  the  induction  coil ;  and  one  from  the  battery  to  the  metal 
of  the  motor,  or  to  "  ground. "  If  the  rotor  of  the  timer  is  insulated 
from  the  metal  of  the  motor,  then  another  wire  for  grounding  the 
rotor,  or  its  ground-ring,  is  necessary. 

58.  Comparison  of  Multi-Induction-Coil  and  High-Tension- 
Distributer  Ignition  Systems.  —  The  high-tension  distribution 
system  has  the  advantage  of  the  absence  of  external  wires  between 
the  timer  and  the  induction  coil  and  of  more  compact  apparatus. 
It  has  the  disadvantage  of  depending  entirely  on  one  induction 
coil  for  the  current  to  all  the  spark  plugs.  In  a  four-cylinder 
motor  the  service  is  so  arduous  that  the  contact  points  of  the 
interrupter  become  very  warm,  and  fusing  and  oxidation  are  of 
frequent  occurrence.  It  is  not  unusual  for  makers  to  construct 
the  case  for  enclosing  the  apparatus  with  space  for  carrying  an 
extra  induction  coil,  and  to  supply  the  extra  coil  as  a  part  of  the 
apparatus. 

When  an  individual  induction  coil  is  used  for  each  spark  plug, 
the  failure  of  one  coil  to  work  does  not  necessarily  stop  the 
motor,  for  it  can  be  run  on  the  remaining  coils  and  their  corre- 
sponding motor  cylinders  and  combustion  chambers.  A  test  can 
also  be  easily  made  to  locate  a  faulty  spark  plug  or  a  cylinder  that 
is  not  acting  properly,  by  holding  down  one  or  more  of  the 
vibrators  and  thus  cutting  out  some  of  the  spark  plugs,  at  the 
same  time  noting  the  action  of  those  left  in  operation.  This 
cannot  be  done  with  the  single  induction  coil  combined  with  a 
high-tension  distributer.  The  high-tension  wires  can  be  dis- 
connected or  short-circuited  in  either  system,  however,  for 
locating  a  faulty  plug  or  cylinder.  This  is  far  less  convenient, 


100  THE   GAS  ENGINE 

and  sometimes  decidedly  uncomfortable  on  account  of  the  elec- 
tric shock  that  may  be  received. 

59.  Jump-Spark  Ignition  in  Two  Cylinders  with  One  Induction 
Coil  and  No  Distributer.  —  In  a  two-cylinder,  four-cycle,  single- 
acting  motor  whose  time  interval  between  explosions  is  of  uniform 
length  (one  revolution  of  the  crank  shaft  apart)  one  induction 
coil  can  be  used  for  ignition  in  both  combustion  chambers. 
The  coil  most  suitable  for  this  purpose  has  four  terminal  binding 
posts  instead  of  three.  This  is  the  usual  construction  of  the 
induction  coil  for  general  uses.  Each  wire  end  of  the  two  wind- 
ings is  terminated  in  a  binding  post  of  its  own,  which  gives  the 
four  binding  posts  or  terminals. 

The  battery  circuit  is  run  as  for  a  single  spark  plug,  but  the 
timer  must  either  turn  at  the  same  speed  as  the  crank  shaft 
or  have  two  stationary  contacts  at  diametrically  opposite  points, 
and  also  have  these  two  contacts  electrically  connected  together 
so  that  the  battery  circuit  is  closed  once  every  revolution  of  the 
crank  shaft.  The  high-tension  circuit  has  a  wire  from  each  of 
the  two  spark  plugs  to  the  corresponding  terminal  of  the  second- 
ary winding  of  the  induction  coil.  The  path  of  the  secondary 
current  is  from  one  terminal  of  the  coil  to  the  insulated  part  of 
the  spark  plug,  when  plugs  having  only  one  side  of  the  spark 
gap  insulated  are  used,  then  across  the  spark  gap  of  the  plug  to 
the  metal  of  the  motor  and  thence  to  the  threaded  bushing  of  the 
other  plug,  then  across  its  spark  gap  to  its  insulated  part  and 
back  to  the  other  binding  post  of  the  secondary  winding  of  the  in- 
duction coil.  Spark  plugs  having  both  sides  of  the  spark  gap  insu- 
lated from  the  motor  metal  require  an  additional  wire  between  the 
plugs,  or  each  must  have  one  side  grounded  to  the  motor  metal. 

The  spark  is  made  in  both  cylinders  simultaneously  and  twice 
as  often  as  it  is  needed.  It  comes  at  about  the  beginning  of  the 
impulse  stroke  and  at  the  corresponding  time  in  the  exhaust 
stroke  or  suction  stroke,  or  between  the  last  two.  When  the 
motor  is  operating  properly  there  is  nothing  but  inert  gases  in 
the  cylinder  whose  piston  is  about  beginning  the  suction  stroke 
at  the  instant  the  spark  passes  in  it,  hence  the  spark  in  that 
cylinder  produces  no  result. 


IGNITION  .101 

But  if  a  charge  fails  to  ignite  at  the  proper  .time  there  will 
be  some  of  the  combustible  mixture  still  remaining  in  the  cylin- 
der when  the  spark  passes  at  about  the  beginning  of  the  suction 
stroke,  and  it  may  be  ignited.  The  result  generally  is  that  it  is 
still  burning  when  the  new  charge  begins  to  enter,  and  the  latter 
is  fired  back  into  the  inlet  pipe  and  carbureter.  This  does  no 
damage  generally,  but  the  motor  does  not  get  another  charge 
of  combustible  mixture  until  after  a  stroke  or  two  of  the  piston 
has  been  made  to  clear  out  the  inert  gases  from  the  inlet  pipes, 
and  there  is  consequently  loss  of  power. 

This  back  firing  into  the  carbureter  occurs  frequently  when 
starting  a  motor  by  cranking,  either  on  account  of  the  failure  to 
fire  a  charge  at  the  proper  time  or  by  the  incoming  charge 
striking  the  spark  plug  at  the  instant  the  spark  jumps. 

This  system  of  ignition  can  be  extended  to  any  even  number  of 
spark  plugs  by  using  one  induction  coil  for  each  pair  of  plugs 
whose  charges  are  to  be  fired  one  revolution  apart. 

The  use  of  this  system  is  decreasing.  It  has  the  objectionable 
features  of  depending  on  only  one  coil  for  two  cylinders  and  the 
absence  of  a  ready  method  of  locating  a  defective  spark  plug  or 
a  cylinder  that  is  not  giving  its  full  power. 

60.  Magneto  Generators  for  Jump-Spark  Ignition.  —  The 
primary  current  for  jump-spark  (high-tension)  ignition  is  very 
often  furnished  by  a  magneto  generator.  Both  the  rotary- 
armature  and  the  oscillating-armature  types  are  used.  The 
rotary  type  generates  an  alternating  current.  There  are  two 
forms  of  the  apparatus  found  in  general  practice. 

The  armature  of  the  magneto  is  usually  of  the  simple  shuttle- 
wound  type  with  the  customary  I-shaped  cross-section  of  armature 
core.  In  the  better  machines  the  armature  core  is  built  up  of  nu- 
merous thin  stampings  from  sheets  of  soft  iron  or  mild  steel.  The 
I-shaped  stampings  are  placed  side  by  side  to  build  up  the  core. 

The  magneto  is  a  separate  piece  of  apparatus  in  one  system 
of  ignition.  The  low-tension  current  from  the  magneto  is  taken 
to  a  transformer  for  changing  it  into  high-tension  current  for  the 
spark-plug  circuit.  The  transformer  is  an  induction  coil  without 
an  interrupter  (trembler,  vibrator). 


102 


THE   GAS  ENGINE 


In  another  system  both  the  magneto  and  the  induction  coil,  or 
transformer,  are  embodied  in  a  single  piece  of  apparatus,  which 
is  commonly  called  a  "high-tension  magneto." 

61.  Low-Tension  Magneto  and  Separate  Transformer  System 
of  Jump-Spark  Ignition.  —  A  magneto  with  either  a  rotary 
armature  or  an  oscillating  armature  can  be  used  in  this  system. 


Circuit  Breaker 

£  | — Contact  Point 


Condenser 


FIG.  52. 

Magneto  and  Transformer  for  Jump-Spark  Ignition.   Interrupted  Armature  Current. 

The  cam  is  either  placed  on  the  armature  shaft  or  driven  at  the  same  speed  as  the 
armature.  The  cam  lifts  the  circuit  breaker  and  breaks  the  armature  circuit  at 
the  contact  points  when  the  current  has  reached  about  its  maximum  value.  The 
sudden  drop  of  current  thus  caused  in  the  primary  winding  of  the  transformer 
induces  a  pressure  in  the  secondary  winding  of  sufficient  intensity  to  make  a  spark 
at  the  ignition  points  of  the  spark  plug. 

The  condenser  has  the  same  function  as  in  an  induction  coil  with  a  vibrator  for 
interrupting  the  primary  current. 

The  figure  is  an  entirely  diagrammatic  representation  of  the  system.  A  cylindrical 
timer  with  non-conducting  segments  for  interrupting  the  current  is  generally 
used  instead  of  a  circuit  breaker  of  the  nature  shown. 


IGNITION 


103 


When  a  rotary  armature  is  used,  the  more  u«ual  practice  is 
to  drive  it  at  a  high  speed,  and  use  a  timer  for  closing  the  primary 
circuit  through  the  transformer  at  the  instant  an  ignition  is 
wanted.  The  rapidly  alternating  current  from  the  magneto 
passes  through  the  primary  (low-tension)  coil  of  the  transformer 
and  induces  a  high-tension  current  in  the  secondary  winding 
which  connects  to  the  spark  plug.  A  series  of  sparks  pass 
at  the  plug  each  time  the  primary  circuit  is  closed  by  the 
timer. 


FIG. -53. 

Magneto  with  Separate  Transformer  for  Jump-Spark  Ignition.     Shunted  or 
Short-Circuited  Primary  Current. 

The  armature  current  is  short-circuited  through  the  contact  points  till  it  has  reached 
about  its  maximum.  The  circuit  breaker  is  then  opened  and  the  consequent 
sudden  increase  of  current  in  the  primary  of  the  transformer  causes  a  spark  at 
the  spark  plug.  Immediate  closing  of  the  circuit  breaker  will  induce  another 
spark  at  the  plug  on  account  of  sudden  decrease  of  current  in  the  primary  of  the 
transformer. 


104  THE   GAS  ENGINE 

With  this  arrangement  the  armature  can  be  driven  by  a  belt, 
friction  gears,  or  friction  clutch,  for  it  is  not  necessary  that  the 
speed  of  the  armature  shall  bear  a  constant  ratio  to  that  of  the 
crank  shaft  of  the  motor. 

If  a  speed-limiting  device  is  used  in  connection  with  the 
friction  gears  or  clutch,  then  the  armature  can  be  given  a  high 
speed  ratio  in  relation  to  the  crank  shaft,  so  that  rotating  the 
motor  shaft  slowly,  as  when  cranking  a  small  motor  by  hand, 
will  generate  current  of  sufficient  volume  and  frequency  to 
induce  a  spark  in  the  combustion  chamber.  The  speed-limit- 
ing device  prevents  the  speed  of  the  armature  from  becoming 
excessive  when  the  motor  rotates  rapidly. 

Some  rotary  magnetos  for  this  system  are  so  constructed  that 
they  can  be  connected  by  a  positive  drive  to  the  motor  crank 
shaft  so  as  to  have  a  constant  speed  ratio  to  the  latter.  The 
armature  is  wound  so  that  it  will  give  enough  current  to  produce 
the  ignition  spark  when  the  motor  is  cranked  rapidly  by  hand, 
and  will  not  be  injured  or  deliver  too  much  current  or  voltage  to 
the  transformer  when  the  motor  runs  fast. 

The  oscillating-armature  magneto  always  gives  the  same 
current  and  voltage,  whatever  the  speed  of  the  motor.  A  timer 
is  not  necessary  in  connection  with  it,  but  is  often  used.  When 
the  timer  is  used  the  transformer  generally  has  a  condenser. 
The  oscillating  magneto  gives  only  one  spark  for  each  ignition. 
Its  armature  is  moved  partly  around  at  a  comparatively  low  rate 
against  the  resistance  of  a  spring,  and  then  allowed  to  snap  back 
to  generate  the  current  for  the  spark  at  the  plug.  Or,  in  other 
designs,  the  armature  is  held  stationary  while  the  part  to  which 
the  spring  is  attached  rocks  over,  and  then  the  armature  is 
released  and  follows  with  a  snap,  first  in  one  direction  and  then 
in  the  other.  The  oscillating  magneto  is  used  successfully  on  very 
high  speed  motors,  such  as  those  on  motor  cycles.  In  a  four- 
cylinder,  four-cycle,  single-acting  motor  having  only  one  mag- 
neto, the  armature  must  snap  over  twice  for  every  revolution  of 
the  crank  shaft.  This  has  been  accomplished  on  the  motor  cycle. 

62.  "  High-Tension  Magneto."  —  This  is  the  commercial 
name  for  a  piece  of  apparatus  which  delivers  high-tension  current 


IGNITION 


105 


to  the  spark  plug  in  jump-spark  ignition  when  its  armature  is 
rotated  at  the  requisite  speed,  or  oscillated.  It  is  really  the 
embodiment,  in  one  apparatus,  of  a  magneto  electric  generator, 
a  condenser,  a  transformer,  a  timer,  and  a  high-tension  current 
distributer.  The  latter  is  needed  only  when  the  motor  has  more 
than  one  combustion  chamber. 

In  one  type,  designed  for  a  four-cylinder,  single-acting  four- 
cycle motor,   or  for  a  two-cylinder,   double-acting  motor,   the 


FIG.  54. 

Magneto  without  Separate  Transformer  for  Jump-Spark  Ignition. 
Magneto  Armature  used  on  Transformer.     Interrupted  Primary  Current. 
The  secondary  coil  is  wound  on  the  armature  core  of  the  magneto  outside  of  the 
primary  coil.     The  primary  current  is  interrupted  by  the  circuit  breaker  when 
at  about  its  maximum  value.     The  sudden  drop  of  current  in  the  primary  coil  of 
the  armature,  together  with  the  action  of  the  magnetic  field,  induces  pressure 
in  the  secondary  coil  great  enough  to  produce  a  spark  at  the  spark  plug.     The 
condenser  may  be  embodied  in  the  magneto,   thus  forming  a  "  high-tension 
magneto." 


106  THE   GAS  ENGINE 

shuttle-wound  armature  is  driven  at  the  same  speed  of  rotation 
as  the  crank  shaft  of  the  motor.  The  armature  delivers  low- 
tension  current  to  a  condenser  of  the  usual  tin-foil  construction; 
a  timer  closes  the  circuit  between  the  condenser  and  the  primary 
winding  of  the  transformer  at  the  time  the  condenser  is  fully 
charged,  which  corresponds  to  the  instant  the  spark  is  required 
for  ignition.  One  end  of  the  secondary  winding  of  the  trans- 
former is  connected  to  a  rotating  high-tension  current  distributer 
arm  that  comes,  at  the  proper  instant,  opposite  the  terminal  of 
a  wire  leading  to  the  spark  plug  where  the  spark  is  wanted. 
The  other  terminal  of  the  secondary  .winding  is  grounded  to  the 
metal  of  the  motor.  The  high-tension  current  jumps  both  the 
slight  gap  at  the  distributer  arm  and  that  at  the  spark  plug  at 
the  same  instant.  The  rotation  of  the  distributer  arm  brings  it 
in  turn  opposite  the  end  of  each  wire  that  leads  to  a  spark  plug, 
so  that  a  spark  is  produced  in  each  combustion  chamber  as 
desired. 

The  apparatus  resembles  an  ordinary  magneto  in  general 
appearance.  It  can  be  constructed  for  any  number  of  cylinders, 
and  the  speed  or  rotation  of  its  armature  and  distributer  arm 
varied  accordingly  in  relation  to  the  crank  shaft. 

When  an  oscillating  armature  is  used  the  timer  can  be 
dispensed  with,  especially  if  the  speed  of  the  motor  is  not 
high.  When  there  is  no  timer  the  condenser  can  also  be 
eliminated. 

An  induction  coil  with  an  interrupted  magnetic  circuit  and 
a  single  winding  of  many  turns  of  wire  can  be  used  for  pro- 
ducing high-tension  current  for  the  spark  plug.  The  coil  can 
be  used  with  or  without  a  timer  and  condenser.  Without  the 
condenser  it  differs  from  the  similar  induction  coil  already 
described  for  low-tension  ignition  only  in  having  a  greater 
number  of  turns  in  the  winding. 

63.  Dynamo -Battery  Ignition  and  Lighting  System.  —  Storage 
battery  "floated  on  the  line."  Direct-current  shunt-wound 
dynamo.  Fig.  55  illustrates  a  method  of  using  a  dynamo  and 
storage  battery  simultaneously  for  supplying  current  for  ignition 
purposes,  and  for  small  lights  also  when  desired.  The  scheme 


IGNITION 


107 


is  a  simplification,  to  some  extent,  of  the  same  method  as  applied 
to  power  and  lighting  purposes  on  a  large  scale. 

The  voltage  of  the  system  is  determined  by  the  battery  within 
slight  variations. 

When  the  voltage  of  the  dynamo  is  higher  than  that  of  the 
battery,  the  direction  of  flow  of  current  is  as  indicated  by  the  full 
arrows.  The  current  from  the  lower  ( + )  brush  of  the  dynamo 
divides,  most  of  it  flowing  out  through  the  lower  line.  The  other 
(very  small)  portion  of  the  current  flows  first  through  the  field 


& 

32  C 

I 

Two-way  Switch 

: 

t                          Hinge, 

^Series  Coil 

J-ShuntCoU 
11  1 

Induction                                               Spring^ 

Coil                                                    *    WvVWv- 

o 

—  .  / 

1  |             ±  —==—  g            Cutout-— 

II  /yyy      MWW) 
0  Cutout  for 

^      ic3c 
II* 

^=>  ( 

V 

•f     a           Contact  Poir 

FIG.  55. 
Dynamo-Battery  Ignition  and  Lighting  System.     Battery  "  floated  on  the  line." 

coil  of  the  generator  and  then  through  the  thin-wire  coil  of  the 
armature  cut-out  and  back  to  the  dynamo.  The  main  part  of 
the  current,  in  the  lower  line,  divides  and  the  different  portions 
flow  through  the  storage  battery  and  lamps,  each  portion  in  its 
own  course.  The  induction-coil  circuit  is  shown  open,  and  will 
not  be  considered  at  present. 

The  current  returning  along  the  upper  line  passes  down  through 
the  armature  of  the  dynamo  cut-out,  through  the  contact  points 
and  around  the  series  coil  of  the  cut-out,  then  back  to  the  dynamo. 
The  currents  in  both  coils  on  the  cut-out  act  in  unison  to  draw 
the  armature  of  the  cut-out  toward  the  core  of  the  magnet 
and  thus  to  keep  the  contact  points  together.  The  current 
flowing  through  the  battery  as  indicated  by  the  full  arrows 
charges  it. 

If  the  dynamo  furnishes  between  the  junction  points,  E  and 
F,  of  the  battery  wires  with  the  main  lines  a  voltage  that  is  just 
equal  to  the  voltage  of  the  battery,  then  no  current  will  flow 
through  the  battery,  but  all  the  current  delivered  by  the  dynamo 


io8 


THE   GAS  ENGINE 


IGNITION 


109 


no  THE  GAS  ENGINE 

to  the  lower  main  line  will  pass  through  the  lights  (induction- 
coil  circuit  open). 

When  the  pressure  between  E  and  F  falls  slightly  below  that 
of  the  battery  terminals,  but  with  the  pressure  at  the  dynamo 
still  higher  than  that  of  the  battery,  which  condition  may 
occur  on  account  of  the  resistance  of  the  circuit  from  E 
through  the  dynamo  to  F,  then  current  will  flow  from  the 
battery,  as  indicated  by  the  broken  arrow,  and  through  the 
lamps,  as  well  as  from  the  dynamo  through  the  lamps. 
The  battery  thus  aids  the  dynamo. 

If  the  pressure  of  the  dynamo  falls  below  that  of  the  battery, 
or  more  correctly,  below  that  between  E  and  F,  then  current  will 
flow  from  the  battery  to  E,  divide  there  and  pass  in  parallel 
through  the  dynamo  and  the  lamps  back  to  the  battery.  The 
current  flowing  back  through  the  dynamo  circuit  in  this  manner 
acts  in  opposition  to  the  shunt  coil  of  the  automatic  cut-out. 
Before  this  back-flowing  current  becomes  great  enough  to  injure 
the  dynamo,  it  weakens  the  cut-out  magnet  to  such  an  extent  that 
the  spring  draws  the  cut-out  armature  away  from  the  magnet  and 
separates  the  contact  points,  thus  breaking  the  circuit  that  leads 
through  the  dynamo  and  battery.  The  battery  continues  to 
supply  current  to  the  lamps. 

By  now  increasing  the  voltage  of  the  dynamo,  as  by  speeding 
it  up,  the  current  through  the  field  coil  of  the  generator  and  the 
shunt  coil  of  the  cut-out  can  be  increased  to  magnetize  the  core 
of  the  cut-out  enough  to  draw  its  armature  in  and  again  bring 
the  contacts  together  to  close  the  dynamo  circuit.  This  is  the 
same  process  as  when  starting  the  dynamo  from  rest. 

The  induction  coil  is  connected  to  the  middle  of  the  battery, 
so  that  only  half  of  the  total  voltage  acts  on  it  when  its  two-way 
switch  is  closed  on  either  contact.  If  the  dynamo  circuit  is  open 
and  the  two-way  switch  is  closed  on  the  lower  contact,  then  the 
lower  half  of  the  battery  furnishes  current  to  the  induction  coil; 
if  the  switch  is  closed  on  the  upper  contact,  the  upper  half  of  the 
battery  furnishes  the  current  to  the  induction  coil.  If  with  the 
latter  position  of  the  switch  the  dynamo  is  put  on-with  enough 
pressure  to  send  current  through  the  battery,  the  current 


IGNITION 


III 


from  E  will  pass  up  to  the  middle  of  the  batfery  and  divide 
there,  so  that  part  will  pass  to  the  upper  line  through  the 
induction  coil  and  part  to  the  same  line  through  the  upper 
part  of  the  battery. 

Small  dynamos  for  this  method  of  ignition  are  made  with  the 
automatic  cut-out  as  a  part  of  the  dynamo.     When  intended  to 


N9  5-S-SWITCHBOARD 


WE  PROVIDE  FOR 
EITHER    BELT,  FRICTION 
OR   GEAR   DRIVE. 


READ   HERE 
VOLTAGE    OF  BATTERY, 
AMPERE    DISCHARGE, 
AMPERE   CHARGE. 


-ONE    SWITCH 
^CONTROLS   IGNITION   AND 
VOLT   AMPEREMETER 


CONNECT   THESE  WIRES  FROM 


=^ 
ATTERY) 


TO  COIL  &  ENGINE  THE  SAME  AS  IF  FROM  ABATTERY. 


BATTERY  FLOATING 
ON  LINE  AND  ACTING 
AS  RESERVOIR. 


AUTOMATIC 
IGNITION  DYNAMO 
WITH  AUTOMATIC  CUT-OUTV 


FIG.  58.     Dynamo-Battery  Ignition  System.     Apple  Electric  Company, 
Dayton,  Ohio. 

operate  in  connection  with  a  variable-speed  motor,  a  governor  is 
used  on  the  dynamo  shaft  to  limit  its  speed  to  that  which  gives 
sufficient  voltage  to  charge  the  battery. 

With  suitably  constructed  batteries  and  a  kick-coil  in  the 
ignition  circuit,  the  above  method  of  supplying  current  can  be 
used  for  low-tension  arc  (make-and-break)  ignition.* 

:  There  are   several  other  conditions  and  refinements  which  might  be 
considered   in  connection   with   this   method    of   supplying   current,   but  is 


112  THE   GAS  ENGINE 

64.  Hot-Tube  Ignition.  —  This  method  of  ignition  was  exten- 
sively used  until  recent  years,  and  is  still  in  some  use  on  con- 
stant-speed motors. 

A  tube  of  metal  or  some  such  material  as  porcelain  or  lava 
is  attached  to  the  cylinder  of  the  motor  so  that  one  end  opens 
into  the  combustion  chamber;  the  outer  end  of  the  tube  is  perma- 
nently closed.  An  external  flame  keeps  the  tube  at  a  red  heat. 
When  a  charge  is  compressed  into  the  combustion  chamber 
some  of  it  is  forced  into  the  open  end  of  the  tube  on  account  of 
the  diminution  of  volume  of  the  inert  gases  contained  in  the  tube 
at  the  beginning  of  compression.  The  combustible  mixture 
thus  forced  into  the  tube  is  ignited  by  coming  into  contact  with 
the  red-hot  inner  surface,  and  the  sudden  expansion  of  the  gases 
in  the  tube,  due  chiefly  to  combustion,  projects  a  flame  into  the 
body  of  the  charge.  The  length  of  the  tube  is  so  proportioned, 
and  it  is  so  heated,  that  ignition  occurs  at  about  the  completion 
of  the  compression  stroke.  The  principal  application  of  hot- 
tube  ignition  is  to  motors  running  at  constant  or  approximately 
constant  speed. 

A  timing  valve  was  used  in  connection  with  the  hot-tube 
igniter  in  English  practice.  The  valve  closed  the  opening  from 
the  combustion  chamber  into  the  tube  until  time  for  ignition. 
The  valve,  of  the  poppet  type,  was  then  lifted  from  its  seat  and 
some  of  the  compressed  charge  in  the  combustion  chamber 
allowed  to  pass  into  the  tube  and  become  ignited.  The  timing 
valve  was  lifted  by  the  action  of  a  cam  or  some  corresponding 
mechanism.  With  the  timing  valve,  the  hot  tube  can  be  used  on 
a  variable-speed  motor. 

The  tubes  were  made  of  various  metals  in  their  earlier  appli- 

believed  that  the  cases  considered  will  make  the  method  clear  enough  for 
the  purpose  at  hand. 

It  may  be  noted,  however,  that  there  is  no  provision  shown  for  auto- 
matically cutting  out  the  battery  when  it  becomes  fully  charged,  in  order 
to  prevent  its  injury  by  overcharging.  Such  a  device,  common  to  all 
larger  work,  is  not  generally  considered  necessary  for  gas-engine  ignition 
outfits.  Fuses  to  prevent  excessive  current  can  of  course  ,be  installed  in 
the  usual  manner.  Automatic  circuit  breakers  for  opening  by  the  action 
of  excessive  current  are  hardly  necessary  above  that  shown. 


IGNITION  1 1 3 

cation.  Platinum  and  other  precious  metals  .were  tried,  but 
their  cost  was  objectionable.  The  friable  tubes  of  porcelain  and 
lava  cracked,  often  without  warning,  and  were  therefore  unsatis- 
factory on  account  of  stopping  the  motor  when  power  was 
needed.  Nickel-steel  hot  tubes  have  finally  proved  the  most 
satisfactory  for  this  method  of  ignition.  They  are  not  particu- 
larly expensive,  last  well,  and  give  ample  warning  when  approach- 
ing the  age  limit. 

The  objections  to  the  hot  tube  are  the  open  flame,  the  deteri- 
oration of  the  tube,  and,  when  the  timing  valve  is  used,  the 
difficulty  of  keeping  it  tight.  When  the  timing  valve  is  omitted 
the  ignition  cannot  always  be  brought  about  at  just  the  instant 
desired,  especially  if  the  motor  is  exposed  to  wind  and  cold. 
Throttling  the  charge  so  as  to  reduce  it  in  quantity  also  affects 
the  time  of  ignition,  especially  if  there  is  no  timing  valve. 

65.  Hot-Metal  Igniter  Heated  by  Internal  Combustion.  - 
This  igniter  for  motors  receiving  a  gaseous  charge  is,  in  one  form, 
a  piece  of  steel  resembling  a  short  section  of  tube  with  a  deeply 
corrugated  or  ribbed  interior.  The  corrugations  are  very  deep, 
and  the  open  space  between  them  is  narrower  near  the  center  of 
the  tube  than  at  a  slight  distance  further  out  toward  the  circum- 
ference. The  igniter  is  heated  by  a  flame  before  starting  the 
motor.  The  compression  of  the  charge  in  the  cylinder  forces 
some  of  the  combustible  mixture  back  into  the  tube  and  against 
the  hot  metal,  which  ignites  it.  The  heat  of  the  combustion  of 
the  gases  thus  ignited  is  sufficient  to  keep  the  igniter  red  hot.  An 
adjustment  makes  it  possible  to  bring  the  mixture  against  the 
igniter  at  the  proper  instant  if  the  amount  of  the  charge  is 
always  the  same  so  that  the  compression  pressure  is  practically 
constant. 

In  connection  with  this  method  of  igniting  may  be  men- 
tioned the  very  simple  expedient  of  having  a  piece  of  metal  pro- 
ject into  the  combustion  chamber  so  as  to  become  hot.  After 
becoming  heated  it  serves  as  an  igniter,  but  the  time  of  ignition 
cannot  be  well  regulated  with  it.  A  bolt  screwed  into  the  piston 
has  been  used  in  this  manner.  The  overheating  of  a  water- 
cooled  motor  when  its  water  circulation  fails  is  another  example. 


114  THE   GAS  ENGINE 

66.  Hot- Wire  and  Platinum-Sponge  Igniters.  —  Ignition  by 
means  of  a  hot  wire  or  a  platinum  sponge  has  been  accomplished, 
but  neither  method  was  found  serviceable  enough  to  warrant  its 
continuance. 

In  the  hot-wire  igniter,  a  short  piece  of  very  thin  wire,  generally 
of  platinum,  was  placed  in  the  combustion  chamber  and  heated 
to  incandescence  momentarily  by  passing  an  electric  current 
through  it  at  the  time  a  charge  was  to  be  ignited. 

The  platinum-sponge  method  depends  on  the  property,  peculiar 
to  platinum,  of  becoming  incandescent  when  placed  in  a  current 
of  combustible  gas.  This  property  is  called  "  catalysis."  The 
sponge,  or  a  number  of  very  thin  platinum  wires,  was  placed 
inside  the  cylinder  where  the  current  of  incoming  gas  would 
strike  it  and  quickly  heat  it  to  a  temperature  that  would  ignite 
the  charge.  The  fouling  of  the  sponge  was  a  serious  objection 
to  its  use.  This  method  is  analogous  to  igniting  the  gas  escaping 
from  an  ordinary  illuminating  jet  by  holding  a  platinum  sponge 
or  a  number  of  pieces  of  very  thin  platinum  wire  in  the  current 
of  the  escaping  gas. 


CHAPTER  IV. 
CONTROL  OF  POWER   AND   SPEED. 

67.  General  Methods  of  Control.  —  There  are  two  fundamental 
methods  of  controlling  the  power  and  speed  of  an  internal-com- 
bustion motor  whose  fuel  enters  the  combustion  chamber  in  the 
form  of  gas  or  vapor,  that  find  general  application  in  general 
engineering  practice.     They  are : 

Variation  of  the  amount  of  fuel  supplied; 
Variation  in  the  instant  of  ignition. 

There  are  several  other  methods  of  regulating  the  speed  and 
power,  but  they  are  wasteful  of  fuel  and  otherwise  undesirable  in 
comparison  with  the  two  methods  just  cited. 

It  may  be  said  that  control  by  variation  of  the  instant  of  ignition 
is  also  wasteful  of  fuel,  and  otherwise  usually  undesirable,  yet, 
under  certain  conditions  in  connection  with  the  operation  of 
variable-speed  motors,  as  those  of  automobiles,  hoisting  machin- 
ery, and,  to  some  extent,  of  boats,  the  control  of  speed  by  this 
method  is  most  convenient  and  desirable  when  used  in  connection 
with  variation  in  the  rate  of  fuel  supply. 

68.  Fuel  Control.    General.  —  Variation  in  the  amount  of  fuel 
is  accomplished  by  two  distinct  methods  in  motors  using  gas  or 
vapor  fuel. 

In  one  method  the  motor  takes  in  either  a  complete  charge, 
or  no  charge  at  all,  of  the  combustible  mixture  during  the 
normal  charging  period.  This  method  is  probably  entirely 
limited  in  practice  to  four-cycle  stationary  motors  operating  at 
as  nearly  a  constant  speed  as  can  be  maintained,  although  it  can 
also  be  applied  to  two-cycle  motors. 

On  account  of  the  form  and  the  method  of  operation  of  the 
mechanism  generally  used  to  accomplish  the  cutting  out  of  a 
charge,  it  is  commonly  known  as  the  "  hit-or-miss "  method. 


Il6  THE   GAS  ENGINE 

The  other  method  is  to  vary  the  amount  of  the  charge  while 
always  allowing  enough  mixture  to  enter  the  combustion  cylinder 
to  ignite  and  produce  an  impulse. 

69.  Fuel  Control  in  Four-Cycle  Gas  or  Vapor  Motor.  —  Both 
the  intermittent  cutting  out  of  a  charge,  method  and  the  reduction 
in  the  amount  of  the  charge  method,  cited  in  the  preceding  section, 
find  general  application  according  to  the  conditions  to  be  fulfilled. 

The  four  customary  ways  of  completely  cutting  out  a  charge, 
all  of  them  hit-or-miss  methods,  are : 

1.  Keeping  the  mixture  inlet   valve  closed  during  the   suction 

stroke  and  also  keeping  the  exhaust  valve  closed  as  usual; 

2.  Keeping  the  exhaust  open  and  holding  the  inlet  valve  closed 

during  the  suction  stroke; 

3.  Leaving  the  exhaust  closed  during  the  regular  exhaust  period 

so  as  to  retain  the  inert  products  of  combustion; 

4.  Keeping  the  gas  valve  closed  while  the  mixture  valve  is  kept 

open  to  admit  air  during  the  suction  stroke. 

The  three  usual  ways  of  diminishing  the  quantity  of  fuel  in 
a  charge  are: 

A.  Throttling  the  mixture; 

B.  Varying  the  length  of  time  that  the  mixture  inlet  valve  is  kept 

open; 

C.  Varying  the  length  of  time  that  the  gas  valve  is  kept  open,  but 

opening  and  closing  the  mixture  valve  at  fixed  times. 

By  combinations  of  the  above  methods  control  for  exceedingly 
variable  demands  for  power  is  accomplished  by  first  diminishing 
the  quantity  of  fuel  admitted  for  each  charge  till  a  certain  con- 
dition is  reached,  and  then  cutting  out  charges  as  by  the  hit-or- 
miss  method. 

70.  Governing  and  Hand  Control.  —  The   power  and   speed 
may  be  controlled  either  by  a  governor  or  by  the  hand  of  the 
operator,  according  to  the  requirements. 

The  governor  is  used  when  the  speed  is  to  be  kept  as  nearly 
constant  as  possible  with  the  degree  of  sensitiveness  that  the 
apparatus  can  attain. 


CONTROL  OF  POWER  AND  SPEED        117 

Hand  control  is  used  on  variable-speed  motors,  as  those  for 
automobiles,  hoisting  machines,  launches,  etc.  It  is  generally 
accomplished  by  throttling  the  mixture  and,  to  some  extent,  by 
varying  the  time  of  ignition. 

Both  governing  and  hand  control  are  used  in  conjunction  on 
variable-speed  motors.  In  this  application  the  mechanical 
governor  limits  the  speed  to  a  predetermined  maximum  and 
maintains  that  speed  as  long  as  the  demand  on  the  motor  for 
power  does  not  exceed  its  capacity  at  the  speed  limit  of  rotation 
to  which  the  governor  is  then  set.  When  the  hand  control  (or 
foot  control)  is  brought  into  use  the  governor  is  put  out  of  action, 
either  partly  or  completely,  as  desired.  Usually  the  movement 
of  the  hand  control  changes  the  speed  limit  maintained  by  the 
governor.  Such  a  governor  is  generally  constructed  so  as  to 
hold  the  speed  fairly  constant  at  the  speed  to  which  it  is  tempo- 
rarily adjusted,  within  the  speed  limits  of  the  motor.  Throttling 
the  mixture  is  the  method  generally  adopted. 

Methods  of  Governing  by  Cutting  out  Full  Charges  of  Fuel  or 
of  Combustible  Mixture. 

71.  Hit-or-Miss  Governing  in  General.  —  This  method  was 
applied  to  the  early  motors  operating  on  the  Otto  cycle,  and 
still  finds  extensive  application  especially  in  small  and  medium 
sized  motors.  The  speed  cannot  be  as  closely  regulated  as  by 
reducing  the  amount  of  the  charge  to  keep  down  the  speed  when 
the  demand  for  power  is  low,  but  is  sufficiently  accurate  for  a 
large  range  of  service. 

This  method  of  governing  gives  the  highest  theoretical  effi- 
ciency of  any,  since  each  charge  admitted  is  a  full  one,  and  the 
compression  is  therefore  always  to  practically  the  same  pressure, 
which  is  the  maximum  pressure  suitable  for  the  fuel.  It  may  be 
remembered  that  the  efficiency  is  higher  the  higher  the  com- 
pression pressure. 

The  usual  means  of  securing  the  hit-or-miss  effect  is  by  the 
use  of  a  part  (called  a  "trigger"  or  "pick-piece"  in  certain 
forms)  whose  position  is  controlled  by  the  governor  in  such  a 


Il8  THE   GAS  ENGINE 

manner  that,  when  the  speed  is  not  in  excess  of  the  normal,  it 
engages  with  other  parts  (or  does  not  engage)  in  such  a  manner 
as  to  cause  the  valves  to  perform  their  functions  regularly. 
But  when  the  speed  exceeds  the  normal  this  part  takes  a  position 
such  as  either  to  cause  the  omission  of  the  movement  of  a  valve 
or  to  modify  its  movement  so  that  no  charge  is  drawn  in  during 
the  suction  stroke  of  the  piston. 

The  device  generally  has  a  pair  of  sharp,  beveled  edges  (knife- 
edges)  where  the  hit-or-miss  occurs,  so  that  when  brought 
together  by  a  very  slight  movement  of  the  governor  the  beveled 
edges  catch  together  and  slip  over  each  other  so  as  to  bring  more 
substantial  parts  into  full  engagement  for  operating  the  valve. 
There  are  numerous  modifications  of  the  hit-or-miss  apparatus. 

A  pendulum  governor  was  used  on  the  early  thrust-rod  valve 
lifters,  and  still  finds  application  on  account  of  its  great  simplicity 
and  consequent  small  cost.  It  is  used  in  its  simplest  form  in 
connection  with  a  .valve  whose  stem  is  horizontal.  The  lift  rod, 
or  the  trigger  attached  to  its  end,  is  hinged  and  supports  a  weight 
that  hangs  below  the  hinge.  The  reciprocating  push  rod  has 
a  tendency  to  carry  the  suspended  weight  with  it,  but  the  inertia 
of  the  weight  causes  it  to  lag  behind  the  rod  and  thus  deflect  the 
trigger  from  its  horizontal  position.  The  lag  and  deflection  are 
increased  as  the  speed  increases  until,  at  the  maximum  speed  of 
the  motor,  the  deflection  is  sufficient  to  cause  the  rod  or  trigger 
to  miss  the  valve  stem  so  that  the  valve  is  not  lifted,  and  thus  a 
charge  of  fuel  is  cut  out. 

In  later  mechanisms  for  hit-or-miss  governing  the  centrif- 
ugal governor  with  weights  rotating  about  a  shaft  is  also  used 
for  moving  the  trigger,  the  cam,  the  cam  roller,  etc. 

One  mechanism  has  a  rotary  cam  with  a  roller  follower. 
Both  the  cam  and  the  follower  have  knife-edge  projections  which 
engage  and  bring  their  lifting  parts  together  when  the  speed  is 
below  normal,  but  clear  each  other  when  it  reaches  the  maxi- 
mum, or  vice  versa. 

72.  Hit-or-Miss  Governing  by  Omitted  Openings  of  the 
Mixture  Inlet  Valve.  Four-Cycle  Motor.  —  This  method  finds 
its  application  generally  in  motors  with  mechanically  operated 


CONTROL  OF  POWER  AND  SPEED         119 

inlet  valves.  The  action  of  the  governor  prevents  the  opening  of 
the  mixture  inlet  valve  when  the  motor  speed  exceeds  the  normal. 
The  exhaust  valve  opens  as  usual  both  before  and  after  the  omis- 
sion of  the  charge. 

Either  the  springs  of  the  inlet  and  exhaust  valves  must  be  strong 
enough  to  hold  the  valves  to  their  seats  during  the  suction  stroke 
when  the  inlet  is  left  closed,  or  additional  means  of  holding  the 
valves  to  their  seats  must  be  provided.  The  degree  of  the  partial 
vacuum  in  the  cylinder  is  greater  at  this  time  than  at  any  other, 
and  the  tendency  of  the  suction  to  open  the  valves  is,  of  course, 
correspondingly  great. 

Since  there  is  no  admission  at  the  time  of  a  cut-out  during  the 
suction  stroke,  there  is  a  partial  vacuum  induced  in  the  cylinder 
at  the  end  of  the  impulse  stroke  (without  the  impulse)  when  the 
exhaust  valve  opens  in  its  regular  operation.  This  causes  a  rush 
of  inert  gases  from  the  exhaust  port  into  the  cylinder  by  which 
foreign  matter  is  apt  to  be  carried  from  the  exhaust  passages 
into  the  cylinder. 

The  speed  at  or  about  the  time  of  the  beginning  of  the  suction 
stroke  determines  how  the  governor  shall  act  regarding  the  open- 
ing or  closing  of  the  inlet  valve.  There  are  about  two  inertia 
strokes  between  the  action  of  the  governor  and  the  beginning  of 
the  following  impulse. 

73.  Hit-or-Miss  Governing  by  Keeping  the  Exhaust  Valve 
Open  during  the  Suction  Stroke.  Four-Cycle  Motor.  —  This 
method  is  used  in  connection  with  an  automatic  inlet  valve.  Very 
little  suction  can  be  produced  by  the  action  of  the  piston  when  the 
exhaust  is  open,  therefore  there  is  little  tendency  to  lift  the  inlet 
valve. 

It  should  be  remembered,  however,  that  if  there  is  a  long, 
straight  pipe  for  carrying  off  the  exhaust  the  inertia  of  the 
rapidly  expelled  gases  may  reduce  the  pressure  in  the  cylinder 
enough  to  open  an  inlet  valve  with  a  weak  spring  and  draw  in 
a  small  amount  of  the  mixture,  but  not  enough  to  be  ignited. 
In  such  a  case  the  fuel  drawn  in  is  simply  passed  through  the 
motor  and  wasted.  The  springs  of  automatic  inlet  valves  are 
apt  to  become  weak  in  service. 


120  THE   GAS  ENGINE 

As  a  precaution  against  the  untimely  opening  of  the  inlet  a 
device  for  holding  the  inlet  valve  to  its  seat  when  the  exhaust 
is  open  is  generally  used.  The  simplicity  of  the  valve  mechan- 
ism for  this  method  of  governing  is  the  chief  feature  that  recom- 
mends it.  The  closeness  of  regulation  is  practically  the  same 
as  with  the  hit-or-miss  mechanically  operated  inlet  valve. 
There  is  a  possibility  of  drawing  foreign  matter  into  the  cylinder 
during  the  suction  stroke  when  the  exhaust  valve  is  open. 

74.  Hit-or-Miss  Governing    by  Keeping    the    Exhaust  Valve 
Closed  during  the  Exhaust  Stroke.     Four-Cycle  Motor.  —  This 
is  simpler  than  either  of  the  two  methods  just  discussed,  since 
there  is  no  need  of  any  locking  device  for  the  inlet  valve.     It 
has  the  objection,  however,  that  the  retained  hot  gases  of  com- 
bustion heat  the  motor  and  destroy  the  lubricant  in  the  cylinder 
more  rapidly  than  when  they  are  allowed  to  escape  at  the  end 
of  the  impulse  stroke. 

75.  Hit-or-Miss    Governing     by    Keeping     the     Fuel    Valve 
Closed,  but  Opening  the  Mixture  Inlet  Valve  to  Admit  Air  during 
the  Suction  Stroke.   Four-Cycle  Motor.  —  The  use  of  this  method 
is  confined  almost  entirely  to  motors  using  permanent  gas  for 
fuel.     It   can,  however,    be    used   by   those   in  which    air    car- 
bureted far  beyond  the  ignition  point  is  mixed  with  pure  air  to 
form  a  combustible  mixture  as  has  been  stated.     But  very  few 
motors  that  first  carburate  the  air  nearly  to  saturation  and  then 
dilute  it  are  found  in  use. 

An  additional  valve  for  the  fuel  is  required.  It  generally  opens 
into  the  air  passage,  or  mixing  chamber,  near  the  mixture  inlet 
valve,  and  in  such  a  manner  as  to  cause  the  gas  and  air  to  mix 
quite  thoroughly  before  entering  the  cylinder.  The  mixture 
valve  is  opened  for  every  suction  stroke. 

This  method  of  governing  has  an  undesirable  property  that 
is  peculiar  to  it  and  is  most  marked  when  the  mixture  is  some- 
what too  rich  in  fuel  and  the  load  changes  suddenly  from  heavy 
to  light.  Under  these  conditions  the  passage  of  cool  air  through 
the  cylinder  during  the  several  consecutive  cut-outs  that  follow 
the  consecutive  explosions  of  the  heavy  load,  cools  "the  cylinder 
to  some  extent  and  clears  out  the  inert  gases  that  remain  after 


CONTROL   OF   POWER  AND   SPEED  121 

the  exhaust  stroke  immediately  following  the* last  explosion. 
This  allows  a  greater  weight  of  the  mixture  to  enter  when  the 
fuel  valve  is  opened  after  several  cut-outs,  and  the  air  in  the 
cylinder  at  the  beginning  of  the  suction  stroke  mixes  with 
the  incoming  overrich  mixture  so  that  a  more  perfect  mixture 
is  formed  in  the  cylinder.  The  greater  weight  of  fuel,  the  more 
perfectly  proportioned  mixture,  and  the  absence  of  dilution  by 
inert  gases  all  act  to  produce  a  greater  impulse  on  the  piston 
than  is  obtained  when  there  has  been  no  cut-out.  A  greater 
increase  of  speed  during  the  first  impulse  after  several  cut-outs  is 
the  natural  result.  Even  with  a  single  cut-out  the  energy  of  the 
following  explosion  is  greater  than  that  of  one  following  an 
immediately  preceding  explosion. 

76.  Modern  Modified  Method  of  Cutting  out  Charges.  Four- 
Cycle  Motor.  —  At  least  one  modern  gas-engine  builder  has 
introduced  a  cut-out  device  that  reduces  the  objectionable  speed 
variation  of  this  method  to  a  considerable  extent  and  completely 
eliminates  the  drawing  in  of  exhaust  gases.  In  this  method  the 
mechanical  inlet  valve  is  opened  by  a  rotating  cam  with  one  lobe, 
and  the  exhaust  valve  by  an  exhaust  cam  in  the  same  manner. 
They  are  both  attached  to  a  shaft  that  rotates  at  half  the  speed 
of  the  crank  shaft  as  long  as  explosions  are  needed  regularly. 
An  increase  of  speed  throws  the  cam  shaft  out  of  engagement 
with  its  driver,  and  it  remains  at  rest  till  the  speed  falls  below 
normal.  It  is  then  brought  into  engagement  with  its  driver  again 
and  opens  the  valves  as  usual.  The  device  for  driving  the  cam 
shaft  is  of  such  a  nature  that  the  parts  can  be  disengaged  and 
brought  into  engagement  again  during  one  revolution  of  the 
crank  shaft  of  the  motor,  corresponding  to  half  a  revolution  of 
the  cam  shaft.  Therefore,  when  the  motor  is  working  at  almost 
its  full  capacity  and  a  charge  is  cut  out,  the  cam  shaft  will  be 
picked  up  again  after  one  revolution  of  the  crank  shaft,  the 
mixture  valve  opened  and  a  charge  admitted  so  as  to  be  exploded 
after  only  six  strokes  of  the  piston  instead  of  eight  as  with  other 
cut-out  valve  mechanisms. 

The  cam  shaft  is  disengaged  so  as  to  come  to  rest  just  after 
the  exhaust  valve  closes.  The  latter  remains  closed  until  the 


122  THE   GAS  ENGINE 

time  to  open  for  discharging  exhaust  gases  again,  so  there  is  no 
possibility  of  drawing  foreign  matter  into  the  cylinder  from  the 
exhaust  port  and  pipe,  as  with  some  of  the  other  devices  for 
governing. 

Governing  by  Varying  the  Amount  of  Fuel  Admitted  for  an 

Explosion. 

77.  General.  —  The  power  that  is  developed  by  an  explosion 
in  the  cylinder  of  a  motor  is  proportional,  at  least  in  a  measure,  to 
the  amount  of  fuel  that  is  admitted  and  burned  during  the  impulse 
stroke  of  the  piston.     Since  the  impulses  occur  regularly  and  are 
graduated  to  the  amount  required  to  keep  the  speed  constant  in 
this  method  of  governing,  it  is  therefore  the  method  that  gives  the 
closest  speed  regulation. 

There  are  three  methods  by  which  the  amount  of  fuel  admitted 
per  charge  can  be  varied  so  as  to  still  give  a  combustible  mixture 
in  the  cylinder  when  the  charge  has  been  reduced  within  certain 
limits.  The  three  methods  are: 

a.  Throttling  by  partly  closing  the  passage  through  which  the 

mixture  enters  the  cylinder,  or  by  partly  closing  both  the 
air  and  the  gas  passages; 

b.  Varying  the  length  of  time  during  which  the  mixture  inlet 

valve  is  kept  open; 

c.  Varying  the  length  of  time  during  which  the  fuel  valve  is 

kept   open,  and   opening  and  closing  the  air  valve  at 
regular  times. 

78.  Governing    by    Throttling.  —  This    method    finds    more 
general  application  than  any  other.     It  is  adapted  to  both  two- 
cycle  and  four-cycle  motors  using  either  permanent  gas  or  car- 
bureted air  for  fuel.     The  largest  as  well  as  the  smallest  motors 
can   be   successfully    governed    by   throttling.     The   valves    for 
throttling  vary  in  form  from  the  simple  wing  type  or  butterfly 
type   to   somewhat   complicated   ones   that   have   separate   and 
adjustable  passages  for  air  and  gas.     The  simpler  ones  natu- 
rally find  most  application  to  the  smaller  sizes  of  motors,  which, 


CONTROL  OF  POWER  AND  SPEED 


123 


FIG.  59.  f 

Balanced  Throttling  Governor  and  Valve  Mechanism  of  Nash  Gas  Engine. 
National  Meter  Company,  New  York. 

The   air  enters  through  a  hand  proportioning 
valve  i.      The  gas    enters  through  a  sim- 
ilar proportioning   valve  in  the  same  hori- 
zontal plane  as  the  air  valve.     The  gas  inlet 
and  valve  are  not  shown  in  the  illustration. 
The  gas  and  air  mix  in  the  chamber  2  and 
pass  through  the  two 
openings    at  the   disk 
valves    3   and  4   into 
the     duct     5    leading 
to  the    inlet  valve    6. 
The  disk  valves  3  and 
4  are  attached  to  the 
governor  spindle  7. 


Air 


The  amount  of  the  mixture 
admitted  to  the  combus- 
tion chamber  for  a  charge 
is  regulated  by  the  gov- 
ernor. When  the  speed 
increases,  the  governor 
lowers  the  disk  valves  3 
and  4,  thus  partly  closing 
theiropenings  and  cutting 
down  the  amount  of  mix- 
ture admitted. 

The  governor  and 
valve  mechanism 
are  shown  in  the 
lower  part  of  the 
illustration. 

The  exhaust  pipe  8 
is  water  jacketed. 


124 


THE   GAS  ENGINE 


however,  are  not  necessarily  those  of  the  cheapest  form  of  con- 
struction. The  double  valve  arrangement  with  one  valve  for 
fuel  and  one  for  air  is  found  only  on  motors  using  permanent  gas 
and  the  very  limited  number  using  air  carbureted  to  nearly  the 
saturation  point.  A  centrifugal  governor  is  generally  used  to 
move  the  throttle  valve  so  as  to  give  the  required  amount  of 
charge. 


FIG.  60. 

Proportioning,  Mixing,  and  Throttle  Governing  Device  for  Gas  Engine.     The 
Bruce-Merriam- Abbott  Company,  Cleveland,  Ohio. 

The  principal  parts  of  the  device  are: 

An  outer  casing  with  provisions  for  gas  and  air  connections; 

A  ported  bushing  fitting  in  the  casing; 

A  cylindrical  hollow  valve  with  ports  for  gas  and  mixture. 

The  gas  passes  from  the  gas  space  at  the  bottom  of  the  casing  through  the  port  in 

the  bushing  and  up  between  the  bushing  and  valve  to  the  top  of  the  air  space. 

The  gas  then  passes  out  through  the  bushing  and  mixes  with  the  air  flowing  up 

to  the  annular  chamber  marked  "Mixture  of  Gas  and  Air"  in  the  illustration. 

From  there  the  mixture  goes  through  the  numerous  ports  in  the  upper  halves  of 

the  bushing  and  valve  to  the  inside  of  the  valve  and  then  out  at  the  top. 
The  governor  is  connected  to  the  valve  spindle  which  extends  downward  from  the 

bottom  of  the  device.     Increase  of  speed  causes  the  governor  to  lift  the  valve  and 

thus  reduce  the  area  of  the  port  openings. 
The  gas  and   air  are  proportioned   by  moving  the  bent  handle  shown  at  the 

bottom  of  the  illustration.      This  rotates  the  valve  and  changes  the  area  of 

the  gas  ports. 


CONTROL   OF   POWER  AND   SPEED  125 

The  reduction  of  the  charge  causes  a  corresponding  reduction 
in  the  compression  pressure.  Since  the  efficiency  of  the  trans- 
formation of  the  heat  energy  of  the  gas  into  mechanical  energy 
increases  with  increased  compression  pressure,  there  is  a  de- 
crease of  this  efficiency  caused  by  throttling  on  account  of  the 
reduced  compression  pressure  that  accompanies  it.  This  de- 
crease of  efficiency  is  not  so  great,  however,  as  to  counterbalance 
the  advantage  of  the  close  regulation  of  speed  that  can  be  secured 
by  reducing  the  amount  of  the  charge,  as  compared  with  other 
methods,  when  close  regulation  is  desired. 

There  is  always  some  suction  resistance  to  the  motion  of  the 
piston  during  the  charging  stroke  in  a  four-cycle  motor.  This 
resistance  is  increased  throughout  the  stroke  by  throttling.  The 
suctional  resistance  abstracts  mechanical  energy  from  the  motor. 
The  amount  of  energy  thus  abstracted  is  not  entirely  lost,  how- 
ever, for  some  of  it  is  returned  during  the  early  part  of  the  com- 
pression stroke  while  the  pressure  in  the  cylinder  is  still  below 
atmospheric. 

79.  Governing  by  the  Mixture  Inlet  Valve  to  Reduce  the 
Charge.  Four-Cycle  Motor.  —  By  the  use  of  suitable  valve 
mechanism  the  inlet  valve  can  be  opened  at  the  same  time  for 
each  charging  stroke  of  the  piston,  and  its  closure  timed  later  or 
earlier  so  as  to  let  in  more  or  less  mixture  as  the  speed  of  the 
motor  decreases  or  increases.  As  compared  with  throttling, 
practically  the  same  delicacy  of  speed  regulation  can  be  secured 
by  this  automatic  cutting  off  of  the  admission  of  mixture.  The 
loss  of  efficiency  in  the  heat  transformation  into  mechanical 
energy,  due  to  the  reduction  of  the  compression  pressure,  is 
practically  the  same  as-  for  throttling,  but  there  is  not  quite  so 
great  a  waste  of  mechanical  energy  during  the  suction  stroke, 
for  with  the  cut-off  governor  the  mean  value  of  the  resistance 
to  the  motion  of  the  piston  during  the  suction  stroke  is  not  so 
great  as  by  throttling.  This  is  because  in  cut-off  governing 
the  inflow  of  the  mixture  is  not  restricted  during  the  early  part  of 
the  suction  stroke.  There  is  free  flow  until  the  inlet  valve  closes. 
Up  to  this  point  the  suction  resistance  is  only  that  due  to  the 
passage  of  the  gases  through  the  unobstructed  port.  This 


126 


THE  GAS  ENGINE 


16 


FIG.  61. 


CONTROL   OF  POWER  AND   SPEED  127 


FIG.  61.     (See  also  Figs.  62  and  60.) 

Four-Cylinder,  Four-Cycle,  Single- Acting  Gas  Engine.     115  to  200  Horsepower. 
The  Bruce-Merriam-Abbott  Company,  Cleveland,  Ohio. 

1.  Cylinder. 

2.  Piston. 

3.  Inlet  valve. 

4.  Exhaust  valve,  water  cooled. 

5.  Mixture  port. 

6.  Air  intake. 

7.  Gas  intake. 

8.  Mixer  and  throttle. 

9.  Throttle  valve  stem. 

10.  Lever  arm  between  throttle  valve  stem  and  governor. 

11.  Governor  sleeve  or  quill. 

12.  Governor  fly-balls. 

13.  Hand  handle  for  proportioning  mixture. 

14.  Exhaust  gas  main. 

15.  Vertical  shaft  for  transmitting  power  to  valve  mechanism. 

16.  Gear  on  shaft  driven  by  15. 

17.  Gear  on  cam  shaft. 

18.  Cam  shaft. 

19.  Cam. 

20.  Cam. 

21.  Rocker  arm  for  opening  inlet  valve. 

22.  Rocker  arm  for  opening  exhaust  valve. 

As  the  speed  increases  the  governor  lifts  the  throttle  valve  by  means  of  the  stem  9 
and  cuts  down  the  flow  of  mixture  into  the  motor  cylinder,  while  keeping  the 
proportions  of  the  mixture  constant  (constant  quality  mixture). 

The  cooling  water  for  the  exhaust  valve  flows  down  through  the  small  pipe  in  the 
hollow  valve  stem  and  enters  the  valve  at  the  bottom  of  the  hollow  space,  then 
flows  through  the  openings  into  the  hollow  valve  stem  near  the  top  of  the  water 
space  in  the  valve  and  passes  up  and  out  through  the  annular  space  between  the 
inflow  pipe  and  the  walls  of  the  hollow  stern. 


128 


THE   GAS  ENGINE 


CONTROL   OF   POWER  AND   SPEED  129 

suction  resistance,  up  to  the  corresponding  position  of  the  piston, 
is  much  less  than  when  the  inlet  passage  is  throttled.  After  the 
inlet  valve  is  closed,  the  suction  resistance  increases  to  the  end 
of  the  stroke,  where  it  has  the  same  pressure  as  at  the  end  of  the 
throttled  stroke,  if  the  weight  of  the  charge  is  the  same  in  both 
cases.  Here  again  the  resistance  during  the  completion  of  the 
suction  stroke  after  cut-off  is  less  than  by  throttling  during  the 
corresponding  latter  part  of  the  stroke.  The  mechanical  energy 
returned  to  the  motor  by  suction  during  the  early  part  of  the 
compression  stroke  is  the  same  by  both  methods. 

There  is  a  possibility  that  the  temperature  of  the  mixture  at 
the  end  of  the  charging  stroke  is  higher  by  cut-off  than  by  throttle 
governing,  since  in  the  former  the  complete  charge  is  in  the 
cylinder  some  time  before  the  completion  of  the  stroke,  and  is 
therefore  heated  more  than  when  drawn  in  gradually  as  by 
throttling.  The  principal  effect  of  heating  the  mixture  during 
the  charging  stroke  is  to  reduce  the  weight  of  the  charge  and  the 
power  of  the  motor.  The  difference  of  this  effect  in  the  two 
cases  is  hardly  great  enough  to  need  attention. 

80.  Governing  by  the  Fuel  Valve  to  Reduce  the  Charge.  — 
This  method  is  applicable  to  both  two-cycle  and  four-cycle 
motors  using  gas  or  vapor  fuel. 

Its  especial  field  is  the  two-cycle  motor  of  the  type  in  which 
the  air  and  fuel  are  separately  precompressed  in  auxiliary  com- 
pressors to  a  slight  extent,  sufficient  to  force  them  into  the  motor 
cylinder  when  the  exhaust  port  is  opened,  but  it  is  equally  appli- 
cable to  four-cycle  motors.  It  has  already  been  said  of  this 
type  of  motor  that  when  the  piston  is  at  and  near  the  out 
position  the  exhaust  port  is  open  and  the  charge  enters  while 
the  piston  is  at  and  in  the  neighborhood  of  the  extreme  out 
position  and  while  the  exhaust  port  is  open.  Air  is  admitted 
first  to  scavenger  the  cylinder,  and  then  gas  is  also  admitted  to 
mix  with  the  entering  air' in  proportion  to  form  a  combustible 
mixture  just  before  they  enter  the  combustion  cylinder.  The  time 
at  which  the  fuel  valve  opens  is  regulated  in  accordance  with  the 
need  of  fuel  to  maintain  the  speed  of  the  motor.  The  air  and 
fuel  valves,  or  the  air  and  mixture  valves,  close  at  the  same  time, 


130 


THE   GAS  ENGINE 


13 


15 


10 


18 


FIG.  63. 


FIGS.  63  AND  64. 

Valve  Mechanism  of  Gas  Engine.  Governing  by  fuel  valve.  2000  kilowatts 
capacity  in  double-acting  twin  tandem  engine.  (Four  cylinders,  eight  combus- 
tion chambers.)  The  Allis-Chalmers  Company,  West  Allis,  Wisconsin. 

1.  Cylinder, 

2.  Piston. 

3.  Inlet  poppet  valve  for  mixture.     Closed  by  spring. 

4.  Head  on  upper  end  of  inlet  poppet  valve  stem. 

5.  Rocker  arm  pivoted  at  6  and  resting  (through  a  small  sliding  block)  on  5. 

Operated  by  cam  rocker  7. 


CONTROL   OF   POWER  AND   SPEED 


FIG.  64. 

6.  Pin  connection  between  5  and  stationary  part  of  engine. 

7.  Cam-shaped  rocker  pivoted  at  8  and  bearing  on  its  follower  5. 

8.  Pin  connection  between  7  and  stationary  frame  of  engine. 

9.  Double-seated  hollow  gas  valve.     Concentric  with  3.     Spring  closed. 

10.  Head  on  gas  valve  stems. 

11.  Cam-shaped  rocker  resting  on  13  and  pivotally  connected  to  10. 

12.  Pin  connection  between  10  and  n. 

13.  Movable  rest  for  cam  rocker  n.     Partly  supported  by  the  stationary  frame  of 

the  engine. 


OF  THE 

UNIVERSITY 

OF 


132  THE   GAS  ENGINE 

14.  Eccentric  rod  between  rocker  7  and  eccentric  on  18. 

15.  Rod  connection  between  7  and  n. 

16.  Eccentric  strap  on  14  and  on  eccentric  17. 

17.  Eccentric  on  18. 

18.  Lay  shaft  or  half-speed  shaft. 

19.  Rod  connection  between  rest  13  and  an  eccentric  on  the  governor-actuated 

shaft  20. 

20.  Regulating  shaft  or  governor  shaft. 

21.  Governor  rod. 

22.  Hand  grip  for  dropping  13  so  that  the  gas  valve  will  not  lift  (open). 

23.  Valves  for  proportioning  gas  and  air  by  hand. 

24.  Hand  wheel  for  setting  proportioning  valves. 

25.  26.    Electric  igniters. 

27.  Exhaust  poppet  valve.     Water  cooled. 

28.  Head  on  lower  end  of  exhaust  valve  stem. 

29.  Rocker  arm  cam  follower  for  lifting  exhaust  valve  27.     Pivoted  to  stationary 

frame  of  engine  at  30. 

30.  Pin  connection  between  stationary  frame  of  engine  and  29. 

31.  Rocker  cam  for  lifting  29  and  the  exhaust  valve  27.     Pivoted  to  the  stationary 

engine  frame  at  32. 

32.  Pin  connection  between  31  and  the  engine  frame. 

33.  Eccentric  rod  between  the  rocker  cam  31  and  an  eccentric  on  lay  shaft  18. 

34.  Water  space  in  exhaust  valve. 

35.  Water  pipe  for  exhaust  valve  27. 

36.  Water  inlet  to  exhaust  valve. 

37.  38.    Cooling-water  spaces. 

39.    Check  valve  for  starting  with  compressed  air. 

The  governor  regulates  the  amount  of  gas  admitted  for  each  charge  by  raising  and 
lowering  the  rest  13  on  which  the  cam-shaped  lifting  arm  u:  rocks,  and  thus 
varying  the  extent  of  opening  of  the  gas  valve. 

When  the  exhaust  valve  begins  to  open  against  the  pressure  in  the  cylinder,  the  line 
of  contact  between  the  eccentric-driven  rocker  31  and  its  follower  29  is  near  the 
pivot  (fulcrum)  32  where  the  rocking  cam  is  supported  by  the  stationary  frame 
of  the  engine.  This  gives  a  long  lever  arm  for  the  eccentric  rod  33  to  act  on  when 
first  lifting  the  valve  from  its  seat,  and  a  slow  initial  motion  to  the  valve.  As  31 
rises,  the  line  of  contact  between  it  and  29  moves  out  toward  the  pivot  30  of  the 
rocker  29,  thus  giving  an  increasing  speed  of  lift  to  the  valve  relative  to  the  motion 
of  31  and  a  decreasing  leverage  for  33.  The  reverse  occurs  during  the  closing  of 
the  valve,  so  that  it  seats  gently.  Since  the  force  required  to  move  the  valve 
after  it  leaves  its  seat  is  much  less  than  at  the  instant  of  lifting  it  from  its  seat, 
the  decreasing  leverage  as  the  valve  rises  is  of  no  disadvantage  in  the  application 
of  the  lifting  force,  and  is  advantageous  in  giving  the  valve  a  rapid  movement 
after  it  leaves  its  seat. 

The  action  of  the  mixture  inlet  valve  is  the  same  as  that  of  the  exhaust  valve,  and 
that  of  the  gas  valve  mechanism  is  similar  in  a  general  way. 

The  gas  enters  around  the  outside  and  through  the  inside  of  the  shell  gas  valve. 


CONTROL  OF   POWER  AND   SPEED  133 

which  is  invariable  in  relation  to  the  movement  of  the  piston. 
If  the  air  and  combustible  mixture  stratify  in  the  combustion 
cylinder  as  desired,  the  part  next  the  piston  is  filled  with  air  and 
possibly  some  of  the  inert  gases  of  combustion,  and  the  com- 
bustion chamber  is  filled  with  perfect  mixture,  all  at  about 
atmospheric  pressure  before  compression  begins. 

The  igniter  is  located  so  as  to  be  surrounded  by  combustible 
mixture  at  the  instant  for  ignition. 

Since  the  mixture  arranges  itself  in  a  stratum  in  the  cylinder 
at  less  than  full  loads,  the  fuel  can  be  cut  down  to  a  much  smaller 
amount  than  when  the  combustible  charge  is  distributed  through- 
out the  cylinder.  Therefore  close  speed  regulation  can  be  accom- 
plished satisfactorily  for  all  loads  including  very  light  loads  and 
the  friction  load  of  the  motor  alone. 

By  this  method  of  regulation  the  pressure  of  compression  is 
always  kept  the  same,  hence  there  is  no  reduction  in  the  effi- 
ciency of  heat  transformation  into  mechanical  energy  on  account 
of  a  reduced  compression  pressure  corresponding  to  a  light  load, 
as  there  is  when  mixture  alone  is  admitted  to  the  cylinder  in 
amounts  varying  according  to  the  demands  for  power.  This 
is  true  theoretically,  because  the  efficiency  of  the  cycle  remains 
always  the  same  in  a  motor  when  the  initial  and  final  pressures 
of  the  compression  stroke  do  not  change. 

There  is  no  power  loss  on  account  of  suction  resistance  in 
this  case,  but  its  counterpart  appears  in  the  energy  expended 
to  compress  the  air  and  gas  for  forcing  them  into  the  motor 
cylinder. 

As  applied  to  the  four-cycle  motor,  this  method  of  governing 
can  be  used  without  any  auxiliary  compression  cylinders  or 
pumps.  The  suction  of  the  charging  stroke  is  effective  here  as 
in  other  methods  of  governing.  The  mixture  valve  opens  and 
closes  at  invariable  times,  and  the  fuel  valve  is  opened  early 
or  late,  as  the  speed  is  slow  or  fast  within  the  limits  of  the 
sensitiveness  of  governing,  and  closes  at  an  invariable  time. 
The  same  advantage  of  close  governing  on  very  light  loads, 
and  on  motor  friction  load,  obtains  here  as  in  the  two-cycle 
motor. 


134 


THE   GAS  ENGINE 


CONTROL  OF  POWER  AND   SPEED 


a  ? 


136 


THE  GAS  ENGINE 


CONTROL   OF   POWER    AND   SPEED 


137 


FIG.  66. 
Section  through  Cylinder  and  Valve. 


138 


THE   GAS  ENGINE 


FIG.  67. 
Section  on  A-B,  Fig.  65. 


CONTROL   OF   POWER   AND   SPEED 


139 


000000 


0  Q  Q    Q     O    |Q     Q 
h=  - 


140 


THE   GAS   ENGINE 


12 


FIG.  69. 
Valve  closed  for  Compression  and  Impulse  Stroke. 


CONTROL    OF  POWER  AND   SPEED 


141 


FIG.  70. 
Valve  in  Exhaust  Position. 


142 


THE  GAS  ENGINE 


12 


FIG.  71. 
Valve  in  Charging  Position. 


CONTROL  OF  POWER  AND   SPEED  143 

1  FIGS.  64a,  64b,  AND  65  TO  71. 

"  Complete  Expansion  "  Gas  Engine.    Four-Cycle,  Double- Acting  Tandem  600 
Horsepower.      The  Wisconsin  Engine  Company,  Corliss,  Wis. 

1.  Cylinder. 

2.  Piston. 

3.  Water-jacket  space. 

4.  Poppet  valve  for  inlet  and  exhaust.     Stem  extends  down  through  the  bottom 

of  the  valve  cage. 

5.  Cylindrical   valve   with    air,    power  gas,   and   exhaust   ports.     Hollow   stem 

down  nearly  to  bottom  of  valve  cage.     Concentric  with  4. 

6.  Piston  on  bottom  of  poppet  valve  stem. 

7.  Automatic  fuel  cut-off  valve.     Cylindrical.     Concentric  with  4  and  5.     Motion 

regulated  by  governor. 

8.  Ported  tubular  valve  for  proportioning  air  and  gas  by  hand. 

9.  Stationary  bushing  and  poppet  valve  seat. 

10.  Bearings  for  arm  that  lifts  5  and  4. 

11.  Rods  for  moving  cut-off  valve  7.     Operated  by  cam  on  shaft  18. 

12.  Connection  for  pipe  leading  to  13  and  the  combustion  chamber. 

13.  By-pass  valve.     Operated  from  shaft  18. 

14.  Pipe  connection  between  by-pass  valve  13  and  cylinder  space  under  poppet 

valve  piston  6. 

15.  Rocker  arm  for  lifting  valves  4  and  5.     Cam  driven. 

1 6.  Cam  shaft,  lay  shaft,  or  half-speed  shaft. 

17.  Cam  for  operating  valves  4  and  5. 

1 8.  Small  cam  shaft.     Controlled  by  governor. 

19.  Igniter. 

20.  Igniter.     (Shown  only  in  longitudinal  section.) 

21.  Relief  valve  or  snifter  valve. 

22.  Gas  supply  pipe. 

23.  Air  supply  pipe. 

24.  Exhaust  pipe. 

25.  Compressed  air  valve  for  starting  engine. 

26.  Compressed  air  supply  pipe. 

27.  Starting  handle. 

28.  Screw  gear  on  main  shaft  (crank  shaft)  for  driving  cam  shaft  or  lay  shaft  at  half 

speed  of  main  shaft. 

29.  Screw  gear  on  cam  shaft  or  lay  shaft.     Driven  by  28.     29  also  acts  as  an  oil 

pump  for  supplying  lubricating  oil  to  the  main  bearing  of  the  crank  shaft, 
the  main  crosshead,  and  the  crank  pin. 

30.  Governor. 

31.  Main  crosshead.    Not  shown  in  line  illustrations. 

32.  Intermediate  crosshead. 

33.  Rear  crosshead. 

34.  Cooling  water  supply  pipes  to  valve  case,  cylinder,  and  cylinder  heads. 

35>  36,  37-   Water  connections  to  intermediate  crosshead.     Swinging  telescopic 

connections.     For  water-cooling  the  pistons  and  piston  rod. 
In  the  longitudinal  section,  Fig.  65,  the  valves  of  two  combustion  chambers  are 
shown  in  the  positions  for  movement  of  the  pistons  toward  the  crank  shaft  (toward 
the  left).     Combustion  chamber  B   (not  shown)   is  on  the  impulse   (expansion) 
stroke;  A  (not  shown)  is  exhausting;  C  is  compressing;  and  D  is  charging. 


144  THE   GAS  ENGINE 

Enlarged  sectional  views  of  the  valves  are  shown  in  Figs.  69,  70,  and  71  for  the 
three  positions  during  the  different  steps  of  the  cycle.  The  coil  compression  springs 
are  omitted. 

Fig.  69  shows  the  position  of  the  valves  for  one  combustion  chamber  during  the 
charging  and  impulse  strokes.  The  poppet  valve  4  is  closed  and  the  others  have  no 
action  or  function  during  this  time. 

Just  before  the  completion  of  the  impulse  stroke  the  by-pass  valve,  13,  Figs.  65 
and  66,  is  opened  by  cam  action  and  the  pressure  in  the  combustion  chamber  is 
transmitted  through  the  pipe  14  to  9  and  to  the  under  side  of  the  balancing  piston  6 
on  the  lower  end  of  the  stem  of  the  poppet  valve  4.  The  pressure  under  the  piston  6 
almost  balances  that  on  the  top  of  the  poppet  valve.  The  cylindrical,  double- 
ported  valve  5  is  then  mechanically  lifted  by  cam  action  at  an  invariable  position  of 
the  motor  piston,  by  a  rocker  arm  bearing  against  the  trunnions  10.  As  the  cylin- 
drical valve  5  rises  it  carries  the  poppet  valve  4  with  it,  thus  opening  the  port  for 
exhausting. 

Fig.  70  shows  the  position  of  the  valves  of  one  cylinder  for  exhausting.  The  air 
and  gas  ports  are  of  course  closed  during  the  exhaust  stroke. 

At  about  the  end  of  the  exhaust  stroke  the  cylindrical  valve  5  descends  under 
the  combined  action  of  the  expansion  coil  spring  (see  longitudinal  section)  and  the 
cam,  so  that  its  ports  register  with  those  of  the  air  and  gas  ducts  around  the  valves 
just  after  the  beginning  of  the  charging  stroke.  This  position  of  5  is  shown  in  Fig. 
71.  If  the  engine  is  on  only  part  load,  the  gas  cut-off  valve  7  still  retains  the  posi- 
tion shown  in  Fig.  70,  so  that  the  gas  port  is  closed  and  air  only  is  allowed  to  enter 
the  cylinder.  Later  in  the  charging  stroke,  at  a  time  determined  by  the  governor, 
cam  action  allows  the  cut-off  valve  7  to  be  lifted  by  the  expansive  force  of  the  coil 
compression  spring  (see  longitudinal  section)  bearing  against  it,  so  that  the  port 
in  the  cut-off  valve  registers  with  the  gas  port  in  the  cylindrical  valve  5  and  in  the 
bushing  9. 

Fig.  71  shows  the  position  of  the  valves  for  admitting  both  gas  and  air  to  the 
cylinder.  At  the  fixed  time  for  cutting  off  the  admission  of  mixture  to  the  cylinder, 
the  double-ported  valve  5  is  lifted  by  cam  action  to  the  position  shown  in  Fig.  69, 
thus  closing  both  the  air  and  gas  ports. 

Up  to  this  time  since  opening  for  exhausting,  the  poppet  valve  is  held  up  by  the 
exhaust  gases  under  the  balancing  piston  6  on  account  of  throttling  which  prevents 
rapid  escape  of  the  gases  from  under  6.  After  the  mixture  is  cut  off,  the  poppet  valve 
4  settles  to  its  seat  so  as  to  be  closed  at  the  beginning  of  the  compression  stroke. 

The  gas  cut-off  valve  7  is  drawn  down  by  cam  action  at  about  the  same  time  that 
the  cylindrical  valve  5  is  lifted  to  cut  off  air  and  gas. 

At  full  load  the  gas  cut-off  valve  7  rises  early,  so  that  the  admission  of  gas  begins 
at  the  same  time  as  that  of  the  air. 

Summary  of  the  Valve  Motions.  —  The  cylindrical,  double-ported  valve  5  moves 
at  invariable  times  relative  to  the  motion  of  the  motor  piston.  The  poppet  valve 
4  is  lifted  (opened)  at  a  fixed  instant  and  closes  between  the  cut-off  of  the  mixture 
and  the  completion  of  the  charging  stroke.  The  gas  cut-off  valve  moves  to  admit 
the  fuel  gas  at  variable  times  controlled  by  the  governor.  For  full  loads  it  opens 
so  that  gas  is  admitted  as  early  as  the  air,  but  it  opens  later  for  light  loads.  It  does 
not  act  to  stop  the  flow  of  gas,  which  is  done  by  5. 

Cutting  Out  Combustion  Chambers.  —  When  the  load  falls  below  one-fifth  full 
load,  the  governor  automatically  cuts  out  two  of  the  combustion  chambers  by 
leaving  their  gas  valves  closed.  The  engine  then  runs  on  only  two  combustion 
chambers. 


CONTROL  OF  POWER  AND  SPEED         145 

When  the  engine  is  run  for  some  time  on  light  loads,  one  <y  more  of  the  com- 
bustion chambers  can  be  permanently  cut  out  by  hand.  This  is  done  by  locking 
the  exhaust  valve  open. 

Proportioning  Gas  and  Air.  —  The  tubular  shell  8,  outside  of  the  stationary 
bushing  9  that  surrounds  the  valves,  is  rotatable  to  a  limited  extent  by  hand  mechan- 
ism. The  rotary  adjustment  of  8  changes  the  relative  areas  of  the  air  and  gas 
ports  leading  from  the  outer  ducts  to  the  cylindrical  valve  5  and  regulates  the  pro- 
portions of  gas  and  air  in  the  mixture. 

Relief  or  Snifter  Valves.  —  In  order  to  prevent  abnormally  high  pressures  in  the 
cylinder,  each  combustion  chamber  is  provided  with  a  spring-closed  relief  valve  of 
the  same  nature  as  those  used  on  steam  engines  for  allowing  the  escape  of  water 
from  the  cylinder,  or  of  the  nature  of  a  safety  valve  on  a  steam  boiler. 

The  relief  valves  come  into  action  in  case  of  premature  ignition  during  the  com- 
pression stroke. 

Igniters.  —  Each  combustion  chamber  has  two  igniters  of  the  low-tension  make- 
and-break  type.  One  is  placed  in  the  port  at  20  and  the  other  well  up  toward  the 
top  of  the  combustion  chamber  at  19.  This  disposition  insures  dry  contact  points 
on  the  upper  igniter  when  starting  with  cold  cylinders,  and  also  the  ignition  of  the 
charge  by  the  lower  igniter  when  the  engine  is  running  on  a  light  load  with  a  corre- 
spondingly small  amount  of  gas  admitted  at  the  latter  part  of  the  charging  period. 

The  igniters  can  be  removed  and  replaced  in  any  combustion  chamber  while  the 
engine  is  running,  by  locking  the  open  exhaust  valve  of  that  chamber. 

Cooling  Water.  —  The  cooling  water  for  the  cylinders  and  the  exhaust  valves 
enter  below  the  exhaust  valves  and  passes  up  to  the  top  of  the  cylinder  to  the  open 
top  of  an  overflow  pipe.  This  pipe  pierces  the  jacket  casing  of  the  cylinder  near 
the  bottom  and  close  to  the  end  near  the  intermediate  crosshead.  The  portion  of 
the  pipe  between  the  open  overflow  end  at  the  top  of  the  jacket  space  and  the  point 
where  it  pierces  the  jacket  wall  is  inside  the  water  space. 

The  pistons  and  piston  rods  are  cooled  by  water  that  flows  to  the  intermediate 
crosshead  through  oscillating  telescopic  pipe  connections.  A  pipe  in  the  center  of  the 
hollow  piston  rod  leads  the  water  from  the  intermediate  crosshead  to  the  rear  cross- 
head  33.  The  water  flows  back  through  the  space  between  the  central  pipe  and 
the  wall  of  the  hollow  piston  rod  to  the  piston,  then  through  the  piston  and  back  to 
the  outflow  connection  at  the  intermediate  crosshead.  The  other  piston  and  its 
portion  of  the  rod  are  cooled  similarly. 

Lubrication.  —  The  screw  gear  29  on  the  cam  shaft  (lay  shaft)  16  and  under  the 
main  shaft  (crank  shaft)  acts  as  an  oil  pump  for  forcing  streams  of  lubricating  oil 
to  the  main  bearing  of  the  crank  shaft,  the  crank  pin,  and  the  main  crosshead.  The 
gear  is  enclosed  in  a  case  that  fits  a  portion  of  the  periphery  closely,  so  that,  when 
there  is  sufficient  oil  in  the  casing,  the  gears  act  much  as  an  ordinary  gear  pump 
whose  spaces  between  the  teeth  are  the  pockets  that  carry  the  oil  around  in  pump 
action.  The  other  bearings  have  self-oiling  devices  or  run  in  an  oil  bath. 

The  pistons  and  metallically  packed  stuffing  boxes  are  lubricated  with  gas  engine 
cylinder  oil  by  mechanically  driven  sight-feed  pressure  lubricators. 

Starting  the  Engine.  —  The  engine  is  started  by  compressed  air  at  about  125 
pounds  pressure.  A  cam  on  the  governor  shaft  acts  to  admit  the  air  during  the 
impulse  stroke  until  the  pressure  from  combustion  during  this  stroke  is  sufficiently 
great  to  hold  the  air-admission  check  valve  closed  when  the  compressed  air  is  cut 
off  by  shutting  the  main  air  valve. 


146 


THE   GAS  ENGINE 


Governors. 

81.  The  work  to  be  performed  by  the  governor  of  a  gas  or  oil 
motor  is  generally  very  light.  The  governor  can  therefore  be 
small.  Its  sensitiveness  -naturally  depends  on  the  desired 
closeness  of  speed  regulation.  The  centrifugal  type  is  generally 
used  in  forms  analogous  to  those  used  on  throttling  steam  engines 
and  on  those  with  Corliss  or  analogous  valve  gears  for  cutting 
off  steam  at  part  stroke.  An  exception  to  this  practice  is  the 
hydraulic  governor. 


FIG.  72. 
Governor  and  By-Pass  Oil  Valves  for  Hornsby-Akroyd  Oil  Engine. 

The  vertical  pipe  at  the  right  of  the  bevel  gears  is  connected  to  the  discharge  of  the 
fuel  oil  pump.  The  curved  pipe  with  the  glass  sight  (at  the  extreme  right)  leads 
to  the  fuel  oil  tank. 

When  the  speed  of  the  motor  increases,  the  governor  acts  through  the  horizontal 
lever  arm  so  that  the  end  of  the  latter  forces  down  a  small  valve  above  the  end  of 
the  vertical  pipe.  The  opening  of  this  by-pass  valve  allows  a  portion  of  the  oil 
delivered  by  the  pump  to  return  to  the  tank  and  thus  reduces  the  quantity  of 
oil  that  is  forced  into  the  vaporizer.  The  pump  discharge  is  also  connected  to 
the  vaporizer.  If  the  speed  of  the  motor  exceeds  a  certain  limit,  the  governor 
acts  in  the  same  manner  as  before  to  open  a  larger  by-pass  valve  that  is  concen- 
tric with  the  smaller  one  already  mentioned.  The  opening  of  the  larger  valve 
completely  (or  nearly  completely)  cuts  off  the  injection  of  oil  into  the  vaporizer. 

The  speed  to  which  the  motor  is  governed  can  be  changed  by  moving  the  small 
cylindrical  weight  along  the  left-hand  extension  of  the  horizontal  arm. 


CONTROL   OF   POWER  AND   SPEED  147 

82.  Hydraulic  governors  are  used  to  some  extent»on  automobile 
motors   that   have   a   pump  for  circulating  the   cooling  water. 
When  the  speed  of  the  pump  is  proportional  to  that  of  the  motor, 
the  pressure  of  the  water  at  points  near  the  pump  varies  in 
nearly  the  same  proportion  as  the  speed  of  the  motor.     This 
variation  of  pressure  with  variation  of  speed  is  utilized  to  open 
or  close  the  throttle  as  the  speed  of  the  motor  falls  or  rises. 

In  the  more  general  forms  of  hydraulic  governor,  the  water 
acts  against  one  side  of  a  corrugated  diaphragm  to  the  center  of 
which  is  attached  the  mechanism  that  connects  to  the  throttle. 
The  variation  of  the  water  pressure  moves  the  central  part  of  the 
diaphragm,  and  the  motion  of  the  latter  is  transferred  to  the 
throttle. 

The  accuracy  of  governing  in  this  manner  is  not  great,  but 
this  is  not  important  for  variable-speed  motors  operating  under 
the  usual  conditions. 

The  simplicity  of  the  governor  and  the  absence  of  wearing 
parts  are  strong  points  in  its  favor  in  automobile  use,  where 
the  dust  and  grit  that  invariably  reach  bearings  that  are  not 
thoroughly  protected  cause  rapid  wear. 

Hand  Control  of  Speed  and  Power. 

83.  General.  —  The  nature  of  the  requirements  for  variable 
speed  and  power  that  the  motor  must  fulfil  needs  to  be  under- 
stood before  the  control  can  be  studied  comprehensively.     These 
requirements   cover  a  wider  range  in  the  automobile  than  in 
any  other  service. 

In  the  automobile  the  motor  is  called  upon  to  run  at  any  speed 
from  the  highest  permissible  on  account  of  danger  of  its  flying  to 
pieces,  to  the  lowest  at  which  the  inertia  of  the  moving  parts  will 
keep  it  going  between  impulses.  It  is  also  expected  to  deliver 
power  of  varying  amount  up  to  its  full  capacity  for  the  speed  at 
which  it  is  rotating.  When  the  clutch  is  thrown  into  engagement 
to  start  the  car,  the  motor  should,  when  desired,  change  quickly 
from  its  friction  load  to  its  full  capacity  corresponding  to  the 
speed  at  which  it  is  rotating.  When  running  idly  with  the  driving 
gear  disconnected,  it  works  against  its  own  friction  resistance 


148  THE  GAS  ENGINE 

only.  It  must  drop  from  full  load  to  friction  load  quickly,  almost 
instantly,  when  the  friction  clutch  for  transmitting  the  power  is 
suddenly  disengaged,  as  in  an  emergency  at  the  time  the  car  is 
climbing  a  steep  hill  or  rapidly  gaining  speed  on  a  level  road. 
The  motor  is  often  used  as  a  brake  for  retarding  the  speed  of  the 
car,  either  when  stopping  the  car  or  descending  a  hill. 

As  has  already  been  pointed  out,  the  speed  and  power  of  a 
motor  can  be  regulated  either  by  varying  the  amount  of  fuel 
supplied  during  each  charging  stroke  or  by  varying  the  time, 
relative  to  the  position  of  the  piston,  at  which  the  charge  is 
ignited  and  burned.  Except  in  one  or  two  isolated  cases,  variable- 
speed  motors  are  so  constructed  that  both  methods  can  be  applied 
simultaneously. 

Hand  control  of  the  fuel  can  be  effected  by  any  of  the  methods 
that  have  been  given  for  governing.  The  only  change  necessary 
is  the  replacement  of  the  governor  by  a  hand  or  foot  device  for 
regulating  the  supply  of  fuel. 

Governor  and  hand  control  can  both  be  applied  by  connecting 
to  the  governor,  or  the  parts  closely  related  to  it,  a  hand  mechanism 
by  which  the  speed  at  which  the  governor  acts  can  be  varied  at  will. 

Throttling  the  fuel  supply  is,  with  few  exceptions,  the  method 
adopted  for  its  control  in  variable-speed  motors. 

84.  Early  and  Late  Ignition.  Definitions.  —  The  instant  at 
which  the  charge  in  the  cylinder  of  a  motor  is  ignited  can  be 
determined  accurately  in  relation  to  the  position  of  the  piston 
and  crank  when  the  igniter  is  of  the  make-and-break  or  break-and- 
make  type  and  has  the  contact  points  separated  by  the  action  of 
rigid  mechanism  between  it  and  the  crank  shaft  or  piston.  In 
an  igniter  of  this  type  the  contact  points  separate,  for  a  given 
setting,  at  the  same  position  of  the  piston  and  crank  shaft  whether 
the  speed  is  high  or  low. 

When  a  variable-speed  motor  is  running  at  moderate  speed, 
the  ignition  apparatus  is  so  timed  that  the  igniting  arc  will  be 
formed  at  about  the  time  the  piston  has  completed  the  compres- 
sion stroke  and  is  ready  to  start  on  the  impulse  stroke,  in  other 
words,  at  about  the  dead-center  position  of  the  crank:  The  dead- 
center  position  in  the  usual  types  of  motors  is  that  at  which  the 


CONTROL  OF  POWER  AND  SPEED        149 

axes  of  the  crank  shaft,  crank  pin,  and  of  the  piston  pin  or  wrist 
pin  all  lie  in  the  same  plane  and  the  piston  is  at  one  end  of  its 
path  of  travel. 

Under  certain  conditions  of  speed  and  power  the  arc  is  timed 
to  come  earlier  in  the  rotation  of  the  crank,  and  under  other 
conditions  later. 

The  terms  "  early  spark  "  and  "  late  spark,"  or  "  early  igni- 
tion "  and  "  late  ignition,"  are  used  to  designate  the  different 
times  of  ignition.  They  are  only  relative  terms  used  in  a  general 
way.  There  is  no  fixed  boundary  between  early  and  late  igni- 
tion. The  act  of  adjusting  the  ignition  apparatus  to  make 
earlier  ignition  is  called  "  advancing  the  spark,"  and  adjusting; 
for  later  ignition  "  retarding  the  spark." 

The  exact  time  of  separation  of  the  contact  points  of  an  igniter 
varies  in  relation  to  the  position  of  the  piston  in  its  travel  when  the 
force  that  separates  the  contacts  is  transmitted  through  a  spring 
and  the  speed  of  the  motor  varies.  This  is  due  to  the  inertia  of 
the  parts  that  are  actuated  by  the  spring  to  cause  the  separation 
of  the  contacts.  The  lag  due  to  inertia  may  be  of  appreciable 
magnitude  in  comparison  with  the  movement  of  the  piston  at 
high  speeds. 

In  a  similar  manner,  when  an  induction  coil  or  transformer  is 
used  as  a  part  of  the  ignition  apparatus  its  use  makes  it  impossible 
to  determine  at  just  what  position  of  the  piston  and  crank  the 
spark  passes.  This  refers  to  the  usual  outfit  of  a  motor  in 
service. 

When  glowing  hot  surfaces  are  used  to  ignite  the  charge  .there 
is  no  means  of  telling  the  exact  instant  of  ignition. 

85.  Early  and  Late  Ignition  Effects  on  Power  and  Speed.  —  If 
a  variable-speed  internal-combustion  motor  is  running  at  moderate 
speed  under  any  constant  load  with  ignition  at  dead  center,  and 
the  ignition  is  changed  to  come  later  in  relation  to  the  movement 
of  the  parts  of  the  motor,  the  speed  and  power  will  immediately 
drop  if  there  is  no  governor  to  regulate  the  fuel  supply.  Under 
certain  conditions  the  motor  will  take  the  new  speed  and  hold  it 
approximately,  while  the  torque  resistance  to  the  rotation  of  the 
motor  remains  constant  at  the  same  value  as  before  the  ignition 


150  THE   GAS  ENGINE 

was  retarded.  The  power  developed  is  decreased  in  about  the 
same  proportion  as  the  speed  of  rotation.  The  energy  given  to 
the  piston  at  each  impulse  is  the  same  as  it  was  at  the  higher 
speed.  It  is  assumed  that  the  strength,  or  hotness,  of  the 
igniting  arc  or  spark  remains  constant. 

The  reason  that  the  retarded  spark  or  arc  causes  a  decrease 
of  speed  is  that,  with  the  later  ignition,  the  charge  does  not  burn 
early  enough  in  the  stroke  of  the  piston  at  the  higher  speed  to 
give  it  as  great  an  impulse  as  before  retarding  the  ignition,  and 
the  contents  of  the  cylinder  escape  at  a  higher  pressure  and 
temperature  than  with  the  earlier  ignition.  But  when  the  speed 
falls,  inflammation  and  combustion  are  both  completed  earlier 
in  the  stroke,  so  that  the  resulting  mean  pressure  is  higher  and 
the  gases  expand  through  a  greater  portion  of  the  stroke  after  the 
charge  has  completely  burned. 

By  retarding  the  ignition  still  more,  the  speed  and  torque 
will  both  be  decreased.  With  late  ignition  and  a  greatly  re- 
duced speed,  the  charge  will  still  be  burning  when  the  exhaust 
port  is  opened.  When  the  ignition  is  extremely  late,  even 
though  the  speed  is  rather  high,  the  exhaust  will  come  out  as  a 
flame.  In  extreme  cases  the  flame  will  be  carried  through  and 
out  of  the  opening  of  an  exhaust  pipe  several  feet  long. 

If  the  ignition  is  now  advanced,  the  speed  and  power  will  be 
increased  until  they  return  to  the  initial  values  when  the  ignition 
reaches  the  dead  center  again.  By  advancing  the  ignition  still 
further,  the  speed  and  power  will  generally  be  still  further  in- 
creased for  a  slight  advance;  they  will  always  be  increased  in  a 
high-speed  motor.  But  still  further  advance  will  cause  a  de- 
crease of  power,  and  if  the  torque  is  still  kept  constant,  as  has  been 
assumed,  the  speed  will  drop.  If  the  ignition  is  advanced  to 
come  very  much  before  dead  center,  the  motor  will  slow  down 
suddenly  and  stop  quickly,  sometimes  with  a  sudden  reversal 
of  rotation  due  to  the  explosion  of  a  charge  before  the  com- 
pletion of  the  compression  stroke  and  the  consequent  driving 
back  of  the  piston  from  the  combustion  chamber  before  dead 
center  is  reached. 

The  increase  of  power  and  speed  caused  by  advancing  the 


CONTROL  OF   POWER  AND   SPEED  151 

ignition  from  the  dead-center  position  to  a  slight  degree  earlier, 
in  motors  other  than  slow-speed  ones,  is  due  to  the  fact  that  the 
early  ignition  gives  the  charge  time  to  become  well  inflamed  by 
the  time  compression  is  complete,  so  that  combustion  is  fin- 
ished early  in  the  impulse  stroke  and  the  mean  pressure  on  the 
piston  is  increased.  But  when  the  advance  becomes  so  great 
that  the  pressure  attained  before  the  completion  of  the  compres- 
sion stroke  comes  so  early  and  is  of  such  intensity  as  to  seriously 
check  the  motion  of  the  piston  and  to  detract  from  the  energy 
that  should  be  transmitted  to  the  piston  during  the  impulse 
stroke,  the  motor  of  course  loses  power.  And  not  only  does  it 
lose  power,  but  heavy  stresses  are  thrown  on  the  parts,  and  if 
there  is  the  slightest  looseness,  or  lost  motion,  in  any  of  the  con- 
nections between  moving  parts,  it  will  be  indicated  by  knock- 
ing, hammering,  or  pounding. 

86.  Time  of  Ignition  as  Affected  by  Degree  of  Compression. 
-  If  a  throttle-regulated  motor  is  running  on  a  light  load  with 
the  ignition  so  timed  as  to  give  the  maximum  power  per  pound 
of  fuel,  and  the  throttle  is  then  opened  either  for  speeding  up  or 
to  meet  the  demands  of  a  rapidly  increasing  load,  there  will  be 
immediate  knocking  in  a  motor  that  has  some  lost  motion,  as 
evidence  that  the  ignition  is  too  early  for  the  higher  compression 
that  accompanies  the  opening  of  the  throttle  and  consequent 
taking  in  of  larger  charges.  The  ignition  must  be  retarded  to 
give  satisfactory  running.  And,  on  the  other  hand,  when  the 
motor  is  again  throttled  for  a  light  load,  the  power  can  be  in- 
creased by  advancing  the  spark  when  the  speed  of  rotation  is 
the  same  as  before. 

The  rates  of  inflammation  and  combustion  are  more  rapid  the 
higher  the  compression  pressure.  They  both  act  to  suddenly 
check  the  motion  of  the  piston  when  ignition  takes  place  before 
the  completion  of  the  compression  stroke,  and  thus  cause  ham- 
mering or  pounding.  When  the  compression  is  high,  knocking 
will  sometimes  occur  before  the  ignition  is  advanced  to  the  time 
that  gives  the  maximum  power  for  the  speed  and  setting  of  the 
throttle.  This  is  seldom  true,  however,  when  the  load  is  light 
and  the  throttle  well  closed. 


152  THE   GAS  ENGINE 

87.  Lag  in  Jump-Spark  Ignition  Apparatus.  —  In  all  the 
various  systems  of  jump-spark  ignition  there  is  a  time  interval 
of  greater  or  less  length  between  the  instant  the  timer  closes  the 
primary  circuit  and  the  passing  of  the  spark  across  the  spark  gap 
inside  the  cylinder  in  the  secondary  circuit.  This  time  interval 
of  delay  in  the  passing  of  the  spark  will  be  called  the  "  lag  "  of 
the  electrical  apparatus. 

When  the  battery  circuit  is  closed  by  the  timer  in  the  battery 
system  of  ignition,  the  current  is  retarded,  in  gaining  its  maxi- 
mum value,  by  the  inductive  resistance  of  the  induction  coil. 
This  induction  resistance  is  due  chiefly  to  the  magnetic  lag  of  the 
soft-iron  core  and  the  reactionary  effect  of  the  current  in  the 
secondary  winding.  This  causes  a  lag  in  the  formation  of  the  first 
spark  at  the  spark  plug,  even  if  a  spark  jumps  before  the  primary 
current  is  broken  by  the  interrupter.  In  most  induction  coils 
no  high-tension  spark  is  formed  until  the  interrupter  breaks  the 
primary  circuit.  When  the  spark  does  not  come  till  the  battery 
circuit  is  broken,  there  is  an  additional  lag  caused  by  the  inertia 
of  the  vibrator  or  interrupter.  The  tofcal  lag  has  a  time  value 
that  is  equal  to  that  of  a  very  considerable  part  of  a  piston  stroke 
in  a  small,  high-speed  motor.  Therefore,  if  the  timer  is  set  to 
give  a  spark  at  the  dead  center  when  the  motor  is  cranked  by 
hand,  the  spark  will  not  jump  till  long  after  the  dead  center  has 
been  passed  when  the  motor  speeds  up.  In  order  to  keep  the 
spark  at  dead  center  at  the  higher  speed,  the  timer  must  be 
advanced  accordingly.  Advancing  the  timer  to  keep  the  spark 
at  the  same  place  in  the  motion  of  the  piston  is  generally,  and 
incorrectly,  called  advancing  the  spark. 

The  difference  in  the  amount  of  advance  of  the  timer  neces- 
sary in  the  make-and-break  low-tension  system,  as  compared 
with  the  jump-spark  system  with  battery  and  induction  coil,  is 
due  to  the  lag  of  the  latter  apparatus.  It  is  not  because  the 
ignition  must  take  place  earlier  in  the  cycle  by  one  method  of 
ignition  than  by  the  other.  The  necessary  advance  of  the  spark 
itself  (not  the  timer)  or  of  the  arc  is  practically  the  same  in  both 
cases  when  their  hotness  does  not  vary  with  the  speed. 

Jump-spark  systems  with  a  transformer  for  raising  the  electric 


CONTROL   OF   POWER  AND   SPEED  153 

tension  all  have  some  lag,  which  is  generally  less  than  for  those 
having  an  interrupter  induction  coil. 

88.  Hand  Control  by  Throttle  and  Spark.  —  In  order  to  bring 
out  as  clearly  as  possible  the  nature  of  the  work  that  must  be 
done  by  the  motor  and  the  methods  of  manipulating  the  con- 
trols, the  operation  of  the  automobile  will  be  taken  up  in  some 
of  its  phases.  It  will  first  be  assumed  that  the  control  is 
entirely  by  hand,  there  being  no  governor  or  safety  device  for 
regulating  the  speed  of  the  motor.  Jump-spark  ignition  with 
a  battery  will  be  considered  first. 

When  the  motor  is  to  be  started  by  hand  cranking,  the  spark 
is  set  at  or  later  than  the  dead  center,  otherwise  the  motor  will 
kick  backward,  with  danger  to  the  operator.  The  throttle  is 
opened  partly.  After  starting,  if  the  motor  is  to  rotate  while 
the  car  remains  still  for  a  while,  the  throttle  is  then  nearly 
closed  and  the  spark  is  set  late  to  give  a  slow  speed. 
The  throttle  should  be  closed  as  far  as  possible  with  still  enough 
opening  to  keep  the  motor  turning  over  slowly.  Just  before 
throwing  the  friction  clutch  into  engagement  to  start  the  car, 
the  throttle  is  opened  to  produce  a  more  powerful  torque  and 
power  to  give  the  car  momentum.  As  the  speed  of  rotation 
increases,  the  timer  is  advanced  to  keep  the  spark  at  least  as 
early  as  at  the  time  of  throwing  in  the  clutch.  The  timer  is 
generally  moved  up  to  give  a  spark  at  least  as  early  as  the 
dead-center  position  of  the  crank.  When  the  motor  gets  well 
up  toward  its  maximum  speed  and  the  transmission  gears  are 
to  be  shifted  so  as  to  give  the  car  more  travel  per  revolution 
of  the  motor,  the  timer  is  retarded  and  the  change  of  gears 
quickly  made.  The  throttle  need  not  be  closed  any  when  the 
gear  shift  is  made  so  quickly  that  the  motor  has  not  time  to 
race. 

When  the  car  is  running  along  a  good,  level  road,  the  throttle 
and  spark  are  adjusted  in  conjunction  till  the  throttle  is  open 
the  least  amount  possible,  and  the  timer  is  advanced  to  the  point 
that  gives  the  best  result.  When  approaching  an  up  grade  or  a 
piece  of  heavy  road  that  is  to  be  passed  over  without  decrease  of 
speed  the  timer  is  gradually  retarded  and  the  throttle  opened  to 


154  THE  GAS  ENGINE 

give  the  requisite  power.  The  more  the  throttle  is  opened,  the  more 
the  timer  must  be  retarded;  but  the  timer  is  always  kept  as  far 
advanced  as  possible  in  order  to  get  the  maximum  power  for  the 
setting  of  the  throttle  without  pounding  in  the  motor.  When 
the  motor  is  new  and  all  the  parts  snugly  fitted,  the  timer  is  set 
up  to  the  position  that  gives  maximum  driving  effort.  If  it  is 
desired  to  pull  the  car  slowly  for  a  short  time  without  changing 
from  the  high-speed  gear,  it  can  be  done  best  by  retarding  the 
timer  till  the  spark  comes  late,  and  opening  the  throttle  well  to 
secure  a  large  torque.  This  method  is  very  satisfactory  so  far 
as  handling  the  car  is  concerned,  but  it  is  wasteful  of  fuel  and 
heats  the  motor  rapidly.  The  exhaust  pipe  will  become  glowing 
hot  after  driving  in  this  manner  for  some  time,  and  the  cooling 
water  will  soon  boil  except  in  very  cold  weather.  If  the  slow 
speed  of  travel  is  to  be  continued  for  some  time,  the  transmission 
gears  should  be  shifted  so  as  to  let  the  motor  turn  over  more 
rapidly  with  the  throttle  well  closed  and  the  timer  far  advanced. 
A  late  spark  makes  the  motor  work  smoothly  and  the  car  easy 
to  handle  on  slightly  varying  grades,  but  the  effects  of  heating 
the  motor  and  destroying  the  exhaust  valves  are  too  seriously 
objectionable  to  admit  of  operating  the  motor  in  this  manner  for 
a  very  long  time,  even  if  the  large  consumption  of  fuel  is  not  a 
consideration. 

When  the  ignition  is  by  a  low-tension  current  from  a  con- 
stant-speed generator,  so  that  the  intensity  of  the  arc  is  always 
the  same,  and  there  are  no  springs  that  will  allow  lag  in  the 
separation  of  the  contact  points,  the  advancing  and  retarding  of 
the  arc  are  exactly  the  same  as  for  the  jump  spark  (not  the 
timer).  It  will  be  remembered  that  the  larger  part  of  the  ad- 
vance and  retard  with  the  jump-spark  system  is  in  the  position 
of  the  timer,  and  not  in  the  instant  of  the  spark  itself. 

In  one  automobile  motor  no  provision  is  made  for  changing 
the  time  of  ignition,  but  the  arc  is  made  stronger  as  the  speed  of 
the  motor  increases.  This  is  accomplished  by  increasing  the 
speed  of  the  generator  as  the  speed  of  the  motor  increases.  The 
ratio  of  the  two  speeds  is  kept  constant,  or  nearly  so.  With 
this  arrangement,  the  advantage  of  slow  speed  and  strong 


CONTROL  OF  POWER  AND  SPEED         155 

pull  cannot  be  secured  by  retarding  the  spark  and  opening  the 
throttle.  A  slow  speed  of  rotation  and  a  strong  pull  are  often 
extremely  desirable  for  a  short  time. 

89.  Combined  Hand  Control  and  Governing.  —  When  a  motor 
is  entirely  controlled  by  hand  (and  foot)  there  are  times  when 
it  is  impossible  for  the  operator  to  perform  all  the  operations 
quick  enough  to  prevent  the  motor  from  racing,  as  in  the  case 
of  suddenly  disengaging  the  clutch  and  applying  both  hand  and 
foot  brakes  to  avoid  an  accident,  or  when  it  is  necessary  to  re- 
lease the  brakes,  throw  on  the  power  and  steer  the  car  quick 
enough  to  get  away  from  a  dangerous  position.  For  this  reason, 
especially  to  avoid  racing  of  the  motor,  and  in  order  to  provide 
means  by  which  a  uniform  speed  can  be  easily  maintained  on  a 
clear  road,  a  governor  is  connected  to  the  throttle  or  other  fuel- 
regulating  device.  The  governor  is  found  on  many  automobile 
motors,  to  a  less  degree  on  launch  motors,  and  sometimes  on 
stationary  motors  for  hoisting,  etc.  Some  motors  are  provided 
with  a  connection  between  the  clutch  and  throttle  such  that  the 
act  of  disengaging  the  clutch  also  partly  closes  the  throttle. 
This,  however,  does  not  keep  down  the  speed  of  the  motor  when 
the  transmission  gears  are  in  neutral  position  and  the  clutch  in 
engagement. 

A  governor  has,  to  a  small  extent,  been  applied  to  the  timer 
to  adjust  it  in  relation  to  the  speed,  but  without  very  satisfactory 
results.  The  governor  for  a  timer  should  advance  and  retard  it 
in  relation  to  both  the  speed  and  the  amount  of  fuel  supplied 
for  a  charge  or  the  degree  of  compression,  instead  of  for  the 
speed  alone. 

The  fuel  governor  is  set,  in  the  usual  practice,  to  keep  the 
speed  at  the  lowest  at  which  the  motor  will  run  well,  and  to  main- 
tain that  speed  from  friction  load  up  to  the  maximum  torque 
capacity  of  the  motor  at  that  speed.  When  a  higher  speed  is 
wanted,  the  hand  control  is  set  for  that  speed,  and  the  governor 
maintains  it  as  before.  In  other  designs  the  governor  ceases  to 
act  as  soon  as  the  hand  control  is  brought  into  action.  This 
latter  method  is  hardly  desirable  for  an  automobile.  An  accel- 
erator foot  lever  for  opening  the  throttle  wide  and  throwing  the 


156  THE  GAS  ENGINE 

governor  out  of  action  quickly  is  generally  provided  for  sudden 
speeding  up  of  the  motor,  or  for  working  it  at  its  full  torque 
capacity  and  the  highest  speed  it  will  take  under  the  load. 

Comparative  Accuracy  of  Methods  of  Governing. 

90.   Speed  Variation    in  Cut-Out-of-Charge  Governing.  —  By 

the  use  of  the  cut-out  mechanisms  of  the  forms  generally  adopted, 
and  which  have  been  described,  the  piston  of  a  four-cycle,  one- 
cylinder,  single-acting  motor  of  the  simpler  type  must  make 
eight  strokes,  corresponding  to  four  revolutions  of  the  crank 
shaft,  between  the  beginning  of  impulses  when  one  charge  only 
is  cut  out  of  a  series. 

If  the  motor  is  working  at  nearly  its  full  capacity,  and  con- 
sequently cutting  out  an  impulse  only  after  several  have  occurred 
in  regular  consecutive  order,  there  will  be  a  considerable  drop 
of  speed  following  the  missed  explosion.  And,  on  the  other 
hand,  if  the  motor  is  running  with  little  or  nothing  more  than  its 
own  frictional  resistance  to  overcome,  there  will  be  several  con- 
secutive cut-outs,  with  a  slowly  decreasing  rotative  speed  and  then 
a  considerable  rapid  increase  of  speed  when  an  explosion  occurs. 

The  total  variation  of  speed  is  not  as  great  when  working 
against  only  the  friction  load  as  when  delivering  power  up  to 
nearly  the  full  capacity  of  the  motor.  The  maximum  speed  of 
the  motor  is  reached  shortly  before  the  completion  of  the  last 
impulse  stroke  preceding  a  cut-out,  and  the  minimum  speed  just 
after  the  beginning  of  the  first  impulse  stroke  following  the 
cut-out. 

The  relative  extent  of  the  speed  variation  under  light  and 
heavy  loads  can  be  shown  mathematically  with  a  close  degree  of 
accuracy.  In  doing  this  it  will  be  assumed,  for  convenience, 
that  the  maximum  speed  is  reached  at  the  completion  of  the  last 
impulse  stroke  preceding  a  cut-out,  and  that  the  minimum  speed 
occurs  just  at  the  beginning  of  the  next  impulse  stroke.  These 
assumptions  do  not  vary  from  the  true  conditions  enough  or  in 
such  a  manner  as  to  affect  the  result  appreciably.  The  same 
motor  will  be  considered  under  both  light  and  heavy  loads. 


CONTROL  OF  POWER  AND   SPEED  157 

It  should  be  remembered  that,  in  this  method  of  governing, 
every  impulse  acting  on  the  piston  is  produced  by  the  combustion 
of  a  full  charge.  It  will  be  assumed  that  all  charges  contain  the 
same  amount  of  fuel;  also  that  the  resistance  opposing  the  crank 
shaft  is  constant.  The  assumption  is  also  made  that  the  speed 
decreases  uniformly  during  the  time  there  are  no  impulses.  This 
is  not  strictly  true,  since  the  inertia  effects  of  the  reciprocating 
parts  and  the  variation  of  pressure  against  the  piston  cause  a 
variable  rate  of  drop.  The  truth  of  the  results  is  not  affected  by 
this  assumption. 

The  discussion  refers  to  a  single-cylinder,  single-acting,  four- 
cycle motor  governed  in  such  a  manner  that  the  time  interval 
between  explosions  when  there  is  a  cut-out  is  never  less  than  the 
time  corresponding  to  four  revolutions  of  the  crank,  and  is  always 
a  multiple  of  four. 

The  following  notation  will  be  used  : 

N  =  any  number  of  strokes  of  the  piston  not  less  than  12 
and  a  multiple  of  4; 

H  =  the  heat  transformed  into  mechanical  energy  and 
delivered  to  the  piston  each  time  a  charge  is  burned 
in  the  motor  cylinder.  A  constant  ; 

W  =  the  sum  of  the  external  work  done  plus  the  friction  loss 

in  the  motor,  both  during  one  stroke  of  the  piston; 

K.E  =  the    kinetic    energy  given   up    by  the  flywheel  and 

other  moving  parts   during   the   longest  series  of 

consecutive  inertia  strokes  of  the  piston. 

When  the  motor  is  running  on  light  load  and  there  is  only  one 
impulse  stroke  during  AT"  strokes  of  the  piston,  then 


and  since  there  are  N  —  1  inertia  strokes  during  the  AT  strokes 
of  the  piston, 

K.E0  =  (N  -  1)  W0  =  (N  -  1)  ~  •  (Light  load.) 


158  THE  GAS  ENGINE 


Again,  when  the  motor  is  carrying  a  heavy  load  and  there  is 
ly  one  cut-out  during  N  strokes  of  the  pis 
impulses  during  the  N  strokes.     Therefore 


only  one  cut-out  during  N  strokes  of  the  piston,  there  are  —  —  1 

4 


and  since  the  maximum  number  of  inertia  strokes  is  7  when  there 
is  only  one  cut-out  during  N  strokes, 

K.Eh  =  7  Wh  =  7  (-  -  l)  ^  -  (Heavy  load.) 

\4          J  N 

The  decrease  of  speed  is  nearly  proportional  to  the  amount  of 
kinetic  energy  given  up  for  the  amount  of  speed  variation  that 
occurs  in  a  governed  motor.  The  ratio  of  the  kinetic  energy 
given  up  in  the  first  case  (light  load)  to  that  given  up  in  the 
second  case  (heavy  load)  is 


K.E0         N 


K.Eh 


When  N  is  given  its  minimum  value  of  12,  corresponding  to 
one  impulse  and  two  cut-outs  for  K.E.0  and  to  two  impulses  and 
one  cut-out  for  K.Eh,  this  ratio  becomes  yj  =  .786. 

And  since  the  speed  variation  in  each  case  is  practically  pro- 
portional to  the  kinetic  energy  given  up,  the  speed  variation  at 
the  light  load  is  only  about  79  per  cent  of  that  at  heavy  load, 
or  the  variation  at  heavy  load  is  about  1.27  times  that  at 
light  load. 

If  N=  40,  corresponding  to  one  impulse  and  nine  cut-outs 
for  K.E0  and  to  nine  impulses  and  one  cut-out  for  K.Eh,  then 
the  ratio  of  the  kinetic  energy  given  up  during  the  39  inertia 
strokes  with  the  light  load  to  that  given  up  during  the  7  inertia 
strokes  with  the  heavy  load  is  f  f  =  .619. 

In  this  case  the  speed  variation  at  light  load  is  only  about 
62  per  cent  as  great  as  at  heavy  load,  or  the  heavy  load  variation 
of  speed  is  about  1.62  times  that  at  light  load. 


CONTROL  OF  POWER  AND   SPEED 


159 


The  nature  of  th&  speed  variations  for  consecutive  strokes  of 
the  piston  is  shown  in  the  diagrams,  Figs.  73  and  74,  for  N  =  40. 
The  diagrams  are  drawn  to  the  same  scale.  The  diagrams  do 
not  show  the  minor  effects  of  compression,  expansion,  reciprocat- 
ing parts,  etc. 

Beginning  at  the  left-hand  side  of  Fig.  73,  which  is  for  the 
light  load,  the  straight  line  inclined  downward  toward  the  right 
indicates  a  uniform  decrease  of  speed.  The  time  for  the  governor 
to  act  is  at  the  completion  of  the  2d,  6th,  loth,  .  .  .  34th,  38th, 

1  impulse  and  9  cutouts  during  40  Strokes  of  Piston 


\ 

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•  —  . 

36   38    0     2     4 

6     8    10    12  14    16   18   20    32 
Strokes 

24   26  28    30   32 

34   36 

38    40    42 

FIG.  73. 

etc.,  strokes  (suction  or  charging  strokes).  The  speed  has  fallen 
below  that  at  which  the  governor  cuts  out  when  the  inclined  line 
crosses  the  vertical  line  that  represents  the  beginning  of  the  38th 
stroke  to  the  left  of  the  zero.  A  charge  is  therefore  taken  in  and 
compressed  during  the  two  strokes  preceding  the  impulse  stroke 
that  begins  at  the  zero  division.  The  speed  is  increased  from 
A  to  B  during  the  impulse  stroke,  and  then  falls  uniformly  during 
the  following  39  inertia  strokes  and  reaches  a  minimum  at  the 
end  of  the  4oth  stroke.  The  speed  has  fallen  below  the  cut-out 
line  at  the  end  of  the  38th  stroke,  so  that  the  inlet  valve  is  opened 
for  this  charging  stroke.  The  impulse  given  during  the  4ist 
stroke  brings  the  speed  up  to  the  maximum  again. 

Now  taking  up  Fig.  74  for  a  heavy  load,  the  last  impulse  of  a 
consecutive  series  of  impulses  increases  the  speed  from  N  to  P 
during  stroke  i  according  to  the  numbering  on  the  diagram. 
The  speed  then  falls  off  uniformly,  as  indicated  by  the  inclined 
straight  line,  but  at  the  beginning  of  the  third  stroke,  as  repre- 


i6o 


THE  GAS  ENGINE 


sented  by  vertical  line  2,  it  is  still  above  that  at  which  the  governor 
cuts  out.  The  charge  is  therefore  cut  out,  and  the  piston  must 
make,  in  all,  seven  inertia  strokes  during  which  the  speed  falls 
to  R  before  another  impulse  begins.  Impulses  are  then  given 
during  every  fourth  stroke,  beginning  with  the  gih  and  ending 
with  the  4 1 st.  The  speed  has  now  again  reached  the  same  value 

9  impulses  and  1  cutout  during  40  Strokes  of  Piston 


peed 


I  ove  which 


governo 


out 


f 


10  12  14  16  18  20  22  24  26  28  30  32  34  30  38  40  42  44  46  48 
Strokes 

FIG.  74. 

as  at  P,  and  the  cut-out  is  repeated.  The  speed  change  from  A 
to  B,  Fig.  74,  and  that  from  P  to  R}  have  a  ratio  of  f  f  as  has 
been  calculated. 

While  the  greatest  total  speed  variation  comes  with  the  heavy 
load,  the  highest  rate  of  variation  occurs  with  the  light  load.  The 
highest  rate  of  variation  takes  place  during  the  impulse  stroke 
with  both  the  light  and  heavy  load.  The  energy  stored  in  the 
moving  parts  during  each  impulse  stroke  is  the  difference  between 
that  given  to  the  piston  by  each  explosion  and  that  abstracted  for 
external  work  and  friction  in  the  motor.  It  is  represented  by  the 
expression 

Heat  energy  stored  in  moving  parts! 
of  motor  by  each  explosion        J 

The  values  of  W  for  the  two  cases  already  considered  are 


w  = 

0      N 


CONTROL  OF   POWER  AND   SPEED  161 

Since  N  is  never  less  than  12,  the  value  of  W^  is  always  less 
than  that  of  Wh.  Therefore  H  —  WQ  is  always  greater  than 
H  —  Wh,  which  indicates  that  there  is  more  energy  stored  in  the 
moving  parts  during  the  impulse  with  the  light  load  than  with 
the  heavy  load. 

Applying  this  to  the  concrete  case  in  which  N  =  40  gives: 

Energy  stored  in  moving  parts  during  one  "1                 „. 
impulse  when  there  is  but  one  impulse      [  =  H 


40      40 


AQ  4O 

during  the  40  strokes 

Energy  stored  in  moving  parts 
during  one  explosion  when 
there  is  but  one  cut-out  dur- 
ing 40  strokes 


These  results  show  that  the  increase  of  speed  during  one 
impulse  stroke  with  the  light  load  is  f  f ,  or  about  1.25  times  that 
of  the  corresponding  increase  with  the  heavy  load. 

91.  Speed  Variation  with  Throttling  Governor.  —  In  this  case 
the  speed  variation  is  very  much  less  than  by  cutting  out  whole 
charges.     The  piston  receives  its  impulses  at  regular  intervals, 
so  there  is  no  long  period  of  inertia  strokes.     The  speed  curves 
for  both  light  and  heavy  loads  are  of  the  same  nature.     The 
accuracy  of  speed  depends  on  the  inertia  of  the  rotating  parts. 

92.  Uniformity  of  Speed   in  Two-Cycle   Governed   Motor.  - 
Since  the  impulses  come  twice  as  often  in  a  two-cycle  motor  as 
in  a  four-cycle  one  when  both  have  the  same  speed  of  rotation, 
the  governing  is  naturally  more  accurate.     This  is  most  marked 
in  motors  with  only  one  combustion  chamber  and  one  piston. 


CHAPTER  V. 

COOLING   THE   MOTOR. 

93.  General.  —  It  has  already  been  stated  that  some  means  of 
cooling  the  parts  of  the  motor  with  which  the  hot  gases  come  in 
contact  is  necessary  to  prevent  their  overheating. 

The  three  methods  adopted  are  water  cooling,  oil  cooling, 
and  air  cooling. 

When  a  charge  is  burned  in  a  motor,  part  of  the  heat  is 
abstracted  by  the  enclosing  walls,  part  is  transformed  into 
mechanical  energy  by  driving  out  the  piston,  and  the  remainder 
passes  out  with  exhaust  gases.  The  only  useful  part  as  far  as  the 
motor  is  concerned,  is  that  transformed  into  mechanical  energy. 

The  cooler  the  confining  walls,  the  greater  the  amount  of  heat 
abstracted  from  the  gases  by  them.  The  transformation  of  the 
heat  of  the  fuel  into  mechanical  energy  is  therefore  the  more 
efficient  the  hotter  the  walls.  From  this  viewpoint  it  is  therefore 
desirable  to  have  hot  walls. 

On  the  other  hand,  the  cooler  the  walls  the  higher  the  pressure 
to  which  the  compression  of  the  charge  can  be  carried  before 
ignition  occurs  by  the  heat  due  to  compression  when  the  air  and 
fuel  are  mixed  before  compressing,  as  is  the  practice  in  all 
modern  motors  using  gas  or  vapor  fuel  and  in  most  oil  motors. 
The  Diesel  oil  motor  is  a  decided  exception  to  the  general  prac- 
tice. The  efficiency  of  heat  transformation  is  higher  the  higher 
the  compression.  On  this  basis  cool  walls  are  desirable. 

There  have  been  many  tests  on  water-cooled  motors  reported 
in  which  it  is  pointed  out  that  when  the  cooling  water  is  kept  at 
or  near  the  boiling  point,  the  efficiency  is  higher  than  when  a 
bountiful  supply  of  cold  water  is  circulated  through  the  water 
jacket.  But  these  tests  all  seem  to  have  been  .made  without 
changing  the  compression  pressure  in  any  of  the  motors  during 
the  test  when  the  change  was  made  from  hot  to  cold  water.  If 

162 


COOLING  THE  MOTOR  163 

the  compression  pressure  had  been  carried  higjier  for  the  cold 
water  than  for  the  hot,  as  can  be  done  by  lengthening  the  con- 
necting rod  so  as  to  decrease  the  ratio  of  the  volume  of  the  com- 
pression space  to  that  of  the  displacement  by  the  piston  per 
stroke,  the  results  would  have  been  different.  How  far  different 
would  depend  on  how  much  higher  the  compression  pressure 
could  be  carried  with  the  cold-water  jacket  without  producing 
ignition  before  the  completion  of  the  compression  stroke. 

The  capacity  of  the  motor  is  lower  the  hotter  the  cylinder  and 
combustion  chamber.  The  hot  metal  of  the  walls  heats  the 
charge  and  expands  it  before  the  compression  stroke  begins  and 
while  the  inlet  port  is  still  open.  This  is  especially  true  when 
the  inlet  port  is  located  so  that  the  cool  incoming  charge  will 
strike  the  hot  exhaust  valve  and  cool  it.  The  expansion  of  the 
mixture  by  heat  reduces  the  weight  of  the  charge  and  therefore 
also  reduces  the  power  that  is  developed  from  it.  The  result  is 
that  motors  working  with  hot  cylinders  develop  less  power  per 
cubic  foot  of  piston  displacement  per  minute  than  those  with 
cooler  cylinders.  In  other  words,  of  two  motors  having  the  same 
diameter  of  piston  and  length  of  stroke,  and  running  at  the  same 
speed  of  rotation,  but  one  having  a  hot  cylinder  and  the  other  a 
cool  one,  the  latter  will  develop  more  power. 

The  distortion  and  deterioration  of  the  parts  in  the  neighbor- 
hood of  the  combustion  chamber'  by  heat,  and  the  difficulty  of 
sufficiently  lubricating  the  hot  parts,  both  limit  the  degree  of 
hotness  at  which  the  motor  will  operate  satisfactorily. 

94.  Air  Cooling.  —  Air  cooling  has  been  found  entirely  satis- 
factory for  small  motors  such  as  are  used  on  motor  cycles  and  air 
ships.  The  movement  of  the  vehicle  generally  brings  enough 
air  in  contact  with  the  external  portions  of  the  heated  parts  to 
keep  them  cool  enough  to  operate.  But  when  a  motor  cycle  is 
moving  in  the  same  direction  as  a  strong  wind  on  a  hot  day  up 
a  long  grade,  the  motor  is  apt  to  become  rather  hot. 

Air-cooled  automobile  motors  up  to  ten -horsepower  capacity 
per  cylinder  in  four-  and  six-cylinder  designs  have  been  oper- 
ated successfully  for  several  years.  In  the  multi-cylinder  motor 
a  fan  is  provided  to  create  a  draft  against  the  radiating  pro- 


1 64  THE   GAS  ENGINE 

tuberances  of  the  heated  part.  In  some  designs  the  fan  merely 
causes  a  circulation  of  air  through  the  space  enclosed  by  the  hood 
that  covers  the  motor.  In  others  the  heated  parts  and  their  pro- 
tuberances are  surrounded  by  a  casing  which  encloses  a  compar- 
atively small  space  so  as  to  form  an  air  jacket  between  the  casing 
and  cylinder,  etc.  A  current  of  air  is  forced  through  the  jacket 
by  a  blower  or  fan. 

When  the  circulation  of  air  is  poor  around  the  cylinder  of  an 
air-cooled  motor,  the  metal  becomes  hot  enough  to  glow  dis- 
tinctly in  moderate  darkness.  The  motor  runs  successfully 
at  this  temperature,  but  the  continuation  of  such  heating  injures 
the  valves,  etc.,  and  very  copious  lubrication  of  the  cylinder  is 
necessary  with  an  oil  that  will  stand  high  temperatures  before 
burning  or  evaporating.  . 

95.  Water  Cooling.  —  By  far  the  greater  proportion  of  auto- 
mobile motors,  practically  all  .small  stationary  motors  and  all 
large  ones,  launch  motors,  etc.,  are  cooled  by  water  or  some 
other  liquid. 

In  the  more  usual  practice  of  cooling  the  cylinder,  water  is 
passed  through  the  water  jacket  and  then  out  through  a  waste 
pipe  or  to  a  cooler  from  which  it  returns  to  the  motor  again.  In 
at  least  one  motor,  however,  the  method  is  different.  In  it  the 
water  is  kept  at  a  constant  level  in  the  jacket  space  of  the  hori- 
zontal cylinder,  so  as  to  surround  about  three-quarters  of  the 
cylinder,  and  there  is  no  water  outlet  from  the  water  jacket. 
As  the  water  is  gradually  vaporized,  the  vapor  passes  out  of  the 
jacket  through  a  pipe  that  leads  it  to  the  inlet  of  the  motor. 
The  water  vapor  mingles  with  the  air  that  is  entering  the  cylin- 
der and  is  carried  in  with  it. 

In  the  true  circulating  system  of  cooling,  the  water  passes 
repeatedly  from  the  motor  to  the  cooler  and  back  to  the  motor, 
and  so  on. 

Whether  the  circulating  system  or  the  waste  system  of  the 
cooling  water  shall  be  adopted  for  a  motor  naturally  depends 
on  conditions  separate  from  the  motor  itself.  On  a  launch  the 
water  is  allowed  to  flow  overboard,  while  on  an  automobile  it 
is  carefully  retained  and  cooled. 


COOLING  THE  MOTOR  165 

It  is  quite  common  practice  to  pass  the  waste  water  into  the 
exhaust  pipe  on  stationary  and  launch  motors.  This  serves 
the  triple  purpose  of  cooling  the  pipe,  silencing  the  exhaust 
to  some  extent,  and  of  preventing  serious  explosions  in  the 
exhaust  pipe  and  its  connections,  in  case  some  of  the  com- 
bustible mixture  is  passed  unburned  through  the  motor  into 
them. 

Thermal  circulation,  in  which  the  heat  from  the  cylinder  walls 
is  utilized  to  move  the  water  in  the  circulating  system,  is  the 
simplest  and  most  economical  method.  In  the  thermal  system, 
the  top  level  of  the  water  in  the  cooling  apparatus  is  higher  than 
the  top  of  the  jacket  space  of  the  motor,  and  the  lower  level  of 
the  water  in  the  cooler  is  above  the  bottom  of  the  jacket  space. 
A  pipe,  or  passage,  carries  the  water  from  the  top  of  the  jacket 
space  to  the  upper  part  of  the  water  in  the  cooler.  The  open- 
ing of  this  pipe  into  the  cooler  must  be  below  the  surface  of  the 
water,  at  least  the  lower  part  of  the  opening  must  be  lower  than 
the  water  level,  and  the  pipe,  should  have  an  upward  incline, 
or  be  vertical,  from  the  motor  to  the  cooler,  so  that  the  water 
always  rises  as  it  passes  through  it  from  the  former  to  the  latter. 
There  should  be  no  downward  bends  in  the  pipe.  The  pipe 
from  the  lower  part  of  the  cooler  to  the  lower  part  of  the  jacket 
space  should  either  be  inclined  downward  from  the  cooler  or 
descend  vertically,  so  that  the  water  will  always  descend  on  its 
way  from  the  cooler  to  the  motor. 

The  operation  of  the  thermal  system  depends  on  the  fact  that 
hot  water  has  less  density,  or  weighs  less  per  cubic  foot,  than 
cold  water,  and  therefore  always  tends  to  rise  to  the  surface. 
The  hot  water  rises  to  the  top  of  the  jacket  space  and  flows  up 
through  the  pipe  to  the  cooler,  while  the  cold  water  from  the  bot- 
tom part  of  the  cooler  flows  through  the  pipe  to  the  bottom  of 
the  jacket  space,  thus  maintaining  circulation. 

If  the  water  in  the  cooler  falls  below  the  opening  of  the  pipe 
from  the  motor  jacket  space  to  an  appreciable  extent,  the  cir- 
culation will  stop. 

In  stationary-motor  practice  the  cooler  can  be  a  tank,  a  barrel, 
a  reservoir,  or  any  simple  form  of  vessel  that  will  retain  the  water. 


1 66  THE  GAS  ENGINE 

since  it  can  be  made  large  enough  to  have  ample  exposed  water 
surface  and  enough  of  its  own  outer  part  exposed  to  the  air  to 
cool  it.  This  is  also  generally  true  of  portable  and,  to  a  con- 
siderable Extent,  of  semi-portable  motors. 

A  radiator  is  used  for  cooling  the  circulating  jacket  water  in 
automobiles.  It  is  placed  at  the  extreme  front  of  the  car  in 
usual  practice.  Numerous  designs  of  radiators  are  used.  The 
object  sought  in  all  the  correctly  designed  ones  is  to  present  as 
large  an  exterior  cooling  surface  to  the  air  and  as  large  an  in- 
terior contact  surface  to  the  water  as  possible  for  the  amount  of 
water  carried,  and  at  the  same  time  to  have  rapid  passage  of  air 
over  the  radiating  or  exterior  surface  of  the  cooler.  It  is  also 
extremely  desirable  to  keep  the  weight  of  the  radiator  as  low  as 
possible. 

Copper,  brass,  and  bronze  are  the  materials  almost  univer- 
sally used  for  automobile  radiators.  Copper,  or  its  alloys,  is 
most  suitable  on  account  of  its  combined  high  capacity  for 
conducting  heat,  ease  of  working  to  form  and  of  soldering,  and 
toughness. 

A  fan  is  generally  used  for  drawing  air  over  and  between  the 
external  surfaces  of  the  radiator.  When  the  fan  is  a  separate 
piece  of  the  apparatus,  it  is  generally  placed  just  back  of  the 
radiator.  The  tendency  of  modern  practice  is  to  utilize  the  arms 
of  the  flywheel  of  the  motor  for  a  fan  by  making  them  vane- 
shaped.  In  such  cases  the  motor  is  completely  enclosed  by  a 
tight  hood  and  a  bottom  pan,  so  that  the  suction  of  the  flywheel 
at  the  rear  of  the  motor  draws  air  in  through  the  radiator  at  the 
front,  allows  it  to  circulate  around  the  motor,  and  then  discharges 
it  under  the  body  of  the  car. 

The  aid  of  a  fan  is  not  generally  required  in  freezing  weather, 
but  it  becomes  an  absolute  necessity  in  hot  weather.  Without 
it  an  automobile  traveling  up  a  long  grade  together  with  a  breeze 
in  the  same  direction  and  at  the  same  speed,  and  in  a  hot  sun, 
will  have  the  cooling  water  boiling  in  a  short  time. 

A  circulating  pump  for  forcing  the  water  to  circulate  rapidly 
through  the  cooling  system  is  generally  used  -  in  automobile 
practice,  especially  in  the  larger,  high-powered  cars.  The  small 


COOLING  THE  MOTOR  167 

quantity  of  cooling  water  carried  (often  not  more  than  three  or 
four  gallons  for  a  forty-horsepower  motor)  makes  it  necessary  to 
circulate  the  water  rapidly.  This  is  largely  due  to  the  fact  that 
the  water  space  in  the  radiator  is  so  limited  that  but  a  very  small 
part  of  the  water  is  contained  in  its  very  narrow  passages,  hence 
the  circulation  must  be  more  rapid  than  thermal  action  will 
produce. 

The  pump  for  circulating  the  water  is  interposed  in  some 
part  of  the  circuit,  generally  in  the  pipe  between  the  bottom  of 
the  radiator  and  the  bottom  of  the  jacket  space.  The  pump 
is  generally  of  the  rotary  type,  since  this  form  will  deliver  a  large 
quantity  of  water  when  of  small  size  and  light  weight.  Two 
types  are  used,  centrifugal  and  positive  action.  The  centrif- 
ugal pump  creates  a  pressure  in  a  measure  proportional  to  its 
speed  of  rotation,  and  the  amount  of  water  that  flows  depends 
on  the  freedom  of  its  passage  through  the  circuit.  The  positive- 
action  pump  is  of  the  nature  of  a  force  pump.  At  every  revo- 
lution it  delivers  a  fixed  and  constant  volume  of  water,  and  the 
pressure  is  proportional  to  the  resistance  of  the  flow  through 
the  circuit.  This  is  true  provided  the  pump  has  no  leakage 
between  the  parts  that  work  together  and  give  the  impulse  to 
the  water.  There  generally  is  considerable  leakage  in  this 
class  of  pumps  as  used  on  automobiles.  The  centrifugal  type 
has  come  to  be  used  more  generally  in  automobile  practice.  It 
is  the  simpler  form,  and  does  not  depend  on  the  absence  of  leak- 
age for  its  satisfactory  operation. 

In  launches,  the  reciprocating  plunger  type  of  circulating  pump 
for  the  cooling  water  is  more  commonly  used  than  the  rotary. 
The  reason  for  this  selection  does  not  seem  plain  when  the  pump 
is  placed  below  the  level  of  the  water  in  which  the  boat  floats. 
It  is,  of  course,  a  simple  and  inexpensive  form  of  pump,  and 
can  be  driven  by  a  crank  or  an  eccentric  instead  of  gear 
wheels. 

96.  Water-Cooled  Pistons  and  Valves.  —  In  the  smaller  sizes 
of  motors  the  heat  is  conducted  away  from  the  piston  and  valves 
by  the  parts  of  the  cylinder  with  which  they  come  in  contact.  In 
single-acting  motors,  the  piston  is  also  cooled  by  the  external  air 


1 68  THE   GAS  ENGINE 

when  the  piston  is  exposed  to  the  air,  as  in  the  usual  forms  of 
single-acting  stationary  motors. 

In  large,  or  even  in  medium-sized  motors,  the  heat  is  not 
carried  away  with  sufficient  rapidity  in  this  manner  to  keep  the 
parts  cool  enough  for  operation.  The  head  of  a  20  inch  diameter 
piston  will  glow  with  heat  after  the  motor  has  been  on  a  heavy 
load  for  some  time,  and  the  exhaust  valve  becomes  hot  and 
distorted  so  as  to  leak.  The  hot  gases  passing  by  it  also  destroy 
the  smoothness  of  the  bearing  surface  that  comes  against  the  seat 
when  the  valve  is  closed. 

Water-cooling  the  piston  becomes  especially  necessary  in 
double-acting  motors,  since  the  piston  receives  heat  on  both  faces 
and  none  of  it  is  exposed  to  the  external  air. 

The  usual  method  of  cooling  the  piston  of  a  double-acting 
motor  is  to  pass  water  in  through  a  pipe  in  the  hole  of  a  hollow 
piston  rod.  The  piston  is  also  made  hollow,  and  the  space  so 
divided  that  the  water  upon  entering  it  flows  around  so  as  to  cool 
its  entire  surface  and  then  flows  out  through  the  hollow  piston 
rod  in  the  space  not  occupied  by  the  pipe  that  carries  the  water 
in.  A  pump  or  a  head  of  water  is  necessary  to  force  the  water 
through  the  piston  and  piston  rod. 

The  cooling  of  the  exhaust  valve  with  water  is  done  in  a  manner 
similar  to  that  for  the  piston. 

97.  Oil-Cooling  the  Motor.  —  Oil  can  be  used  in  the  same  man- 
ner as  water  for  cooling  the  motor  by  circulating  it  through  the 
jacket  space.  This  has  been  demonstrated  in  regular  service  on 
a  considerable  number  of  motors  for  several  years. 

For  motors  that  are  exposed  to  the  cold  when  not  in  operation 
the  use  of  oil  for  cooling  has  great  advantages  over  water. 
Freezing  of  the  water  will  burst  the  jacket  shell  and  other  parts. 
Any  failure  to  drain  it  off  completely  may  be  the  indirect  cause 
of  broken  pipes  and  radiator.  If  there  are  any  pockets  that  do 
not  drain  easily,  this  failure  is  apt  to  occur. 

When  oil  is  used  for  cooling,  the  value  of  the  oil  makes  a  circu- 
lating system  necessary,  A  radiator  and  circulating  pump  can 
be  used  as  for  water. 

"Oil-cooled"  is  often  erroneously  applied  to  air-cooled  motors 


COOLING  THE  MOTOR  169 

under  the  supposition  that  so  much  cylinder  ail  is  required  to 
lubricate  the  cylinder  and  piston  that  it  has  an  appreciable  cooling 
effect. 

98.  Gaskets  and  Packing  Materials.  —  A  gasket  is  a  piece  of 
comparatively  soft  material,  generally  thin  and  flat,  placed  between 
two  harder  surfaces,  generally  metallic,  for  making  a  tight  joint. 

Where  the  temperature  is  high,  as  where  the  parts  are  heated 
by  exhaust  gases,  the  gasket  must  be  of  a  material  that  will  not 
burn,  and  should  also  be  soft  and  thick  enough  to  allow  for  warp- 
ing of  the  connected  parts.  Asbestos  woven  into  a  sheet,  together 
with  a  net  of  small  copper  wires  for  strengthening,  is  much  used. 
The  material  can  be  easily  cut  to  the  form  needed.  Asbestos 
covered  with  sheet  copper  and  made  up  into  forms  to  be  used 
(rings,  ovals)  is  convenient  and  good. 

When  gasoline  or  naphtha  comes  in  contact  with  the  gasket,  as 
in  an  inlet  pipe,  some  material  that  is  not  affected  by  the  naphtha 
or  gasoline  should  be  used.  Rubber  will  not  do  on  account  of 
the  softening  action  of  the  gasoline  or  naphtha,  but  leather,  wood 
fiber,  paper,  lead,  and  soft  copper  are  suitable. 

For  joints  in  the  cooling-water  connections,  any  of  the  last 
mentioned  materials,  or  any  good  steam  gasket  material,  will 
answer  if  there  is  no  oil  or  other  substance  in  the  water  that  will 
attack  them.  Rubber  and  rubber  composition  should  not  be 
used  when  oil  is  present,  as  in  a  non-freezing  mixture,  or  when 
oil  alone  is  used  as  in  oil-cooled  motors. 

The  pipe  for  the  liquid  fuel  is  generally  very  small.  Lead  or 
soft-copper  rings  serve  well  in  it  for  packing,  but  the  lead  ring 
should  be  quite  thin  so  that  there  is  not  enough  material  to  be 
squeezed  out  so  as  to  close  the  passage.  Vulcanized  wood  fiber 
does  well  here.  The  small  joints  are  generally  ground  to  a  fit. 
If  a  ground  fit  in  the  fuel-pipe  connection  cannot  be  made  tight 
without  packing  or  some  other  filling  material,  a  thin  coating  of 
cake  soap  or  some  rubber  cement  put  between  the  ground  sur- 
faces will  generally  stop  a  leak. 

When  the  joint  remains  dry,  and  especially  if  it  is  highly 
heated  in  service,  it  can  be  prepared  for  easy  separation  by  coating 
one  side  of  a  non-metallic  gasket  with  powdered  or  flake  graphite 


170  THE  GAS  ENGINE 

(plumbago,  black  lead)  and  the  other  side  with  varnish.  The 
varnished  side  will  adhere  so  as  to  hold  the  gasket  in  place,  but 
the  graphite-coated  side  will  separate  readily  from  the  surface 
that  was  pressed  against  it. 

99.  Pump  Packing.  —  Some  fibrous  material  is  generally 
used  for  packing  the  circulating  pump.  Flax  (tow)  is  probably 
best  for  a  water  pump,  but  cotton  wicking  covered  with  graphite 
grease  is  good.  The  latter,  or  prepared  steam  packing  (without 
any  rubber),  does  well  for  the  circulating  pump  of  an  oil-cooled 
motor. 


CHAPTER  VI. 

LUBRICATION   OF  MOTOR. 

loo.  Oils  and  Methods  of  Applying.  —  Copious  lubrication  of 
the  piston  of  an  internal-combustion  motor  is  an  absolute  neces- 
sity. In  the  absence  of  lubrication,  the  rubbing  surfaces  of  the 
piston  and  the  bore  of  the  cylinder  become  dry  and  abrade 
each  other,  and  may  even  seize  together.  As  a  result  the  motor 
loses  power  and  finally  stops.  Oil  is  used  for  lubricating. 

The  oil  to  be  most  suitable  must  withstand  a  high  temper- 
ature without  decomposition  or  rapid  vaporization,  and  when 
finally  evaporated  and  burned  must  leave  a  minimum  deposit 
on  the  walls  of  the  cylinder  and  piston,  valve  stems,  and  ignition 
apparatus.  It  must  also  be  free  from  acids  that  act  on  the 
metal  of  the  motor.  Most  of  the  oils  used  are  thin  (not  vis- 
cous) and  flow  readily,  especially  those  for  small  motors.  In  the 
latter  it  is  often  desirable  to  use  the  same  oil  for  the  bearings 
on  the  crank  shaft  as  for  the  piston. 

One  of  the  simplest  methods  of  lubricating  the  piston  and 
crank-shaft  bearings  of  a  vertical  motor  is  the  splash  system. 
In  it  the  enclosed  crank  case  is  kept  partly  filled  with  oil  to  such 
a  level  that  the  rotating  parts  strike  it  and  splash  it  up  into  the 
bore  of  the  cylinder  and  against  the  piston.  The  latter  is  amply 
lubricated  by  this  method. 

In  order  to  prevent  too  copious  lubrication  of  the  piston  by 
splashing  in  this  manner,  a  splash  plate  is  sometimes  placed 
across  the  lower  end  of  the  cylinder  between  it  and  the  crank 
case.  The  splash  plate  has  a  slot  in  it  only  large  enough  to 
allow  the  movement  of  the  connecting  rod.  No  oil  is  fed  in 
through  the  cylinder  walls  in  the  best  practice  when  the  splash 
system  is  used.  The  lowest  piston  ring  is  sometimes  beveled  on 
the  lower  part  of  the  periphery  so  that  the  oil  will  pass  up  by  it  on 
the  downstroke  of  the  piston.  The  upper  side  is  left  with  a 

171 


1/2 


THE  GAS  ENGINE 


FIG.  75. 

Axial  Section  of  Cylinder  of  Vertical  Gas  Engine.     Four-cycle,  Single-Acting, 
Water- Cooled.    Oil  Well  at  Bottom  of  Cylinder.    Auxiliary  Exhaust  Port. 


A.  Mixture  inlet. 

B.  Exhaust  passage. 

C.  Exhaust  pipe  connection. 

D.  Auxiliary  automatic  exhaust  port. 

E.  Jacket-water  inlet.    Outlet  at  top  of 

jacket  space  not  shown. 

F.  Annular  oil  well  into  which  piston 

dips. 

G.  Piston. 

H.    Combustion  part  of  cylinder. 


J. 
K. 
M. 
N. 
O. 
P. 

Q- 


Opening  for  relieving  compression 
during  first  part  of  compression 
stroke  when  starting.  Ordinarily 
closed  by  valve. 

Connecting  rod. 

Water-jacket  space. 

Flywheel. 

Inlet  valve. 

Exhaust  valve. 

Closing  spring  for  inlet  valve. 

Closing  spring  for  exhaust  valve. 


LUBRICATION  OF  MOTOR 

sharp  corner  so  that  the  oil  will  be  carried  up  on  the  upstroke. 
This  practice  does  not  seem  necessary,  however.  It  is  not 
found  in  very  many  motors. 

Forced  lubrication  is  a  still  more  certain  way  of  securing  posi- 
tive lubrication  of  the  parts.  In  this  system  a  small  pump  is 
used  to  take  the  oil  from  the  bottom  of  the  crank  case  and  force 
it  through  pipes  or  passages  in  the  case  leading  to  the  bearings 
and  thence  through  the  hollow  crank  shaft  and  passages  in  the 
cranks  to  the  crank  pins  and  then  through  the  hollow  connect- 
ing rod  up  to  the  piston  pin  or  wrist  pin.  The  oil  escapes  through 
the  various  bearings  and  runs  back  to  the  crank  case  to  be 
pumped  through  the  system  again.  Both  reciprocating  plunger 
and  rotary  pumps  are  used  for  circulating  the  oil.  Positive-acting 
rotary  pumps  are  more  suitable  here  than  for  water  circulation, 
since  the  copious  lubrication  prevents  rapid  wear  and  conse- 
quent leakage. 

Ring  oiling  of  the  crank-case  bearings  that  support  the  crank 
shaft  is  frequently  adopted.  The  usual  method  is  to  make  the 
bearing  with  an  oil  reservoir  beneath  it,  and  to  cut  away  part  of 
the  top  of  the  bearing  in  order  to  hang  a  ring  over  the  shaft  so 
that  its  lower  part  dips  into  the  oil  in  the  reservoir.  The  weight 
of  the  ring  resting  on  the  top  of  the  shaft  causes  the  ring  to  turn 
when  the  shaft  is  rotating,  but  at  a  slower  rate.  The  rotation 
of  the  ring  carries  oil  up  to  the  shaft,  so  that  the  bearing  is  lubri- 
cated as  long  as  there  is  enough  oil  in  the  reservoir  for  the  ring 
to  touch  it. 

In  horizontal  motors  oil  is  fed  in  at  the  top  of  the  cylinder. 
This  is  the  only  way  the  oil  is  supplied  in  open-frame  motors. 
But  when  the  crank  case  is  enclosed  there  is  some  lubrication 
of  the  piston  by  the  oil  that  flies  from  the  crank  and  connecting 
rod. 

When  there  is  no  pump,  as  for  forced  lubrication,  the  oil  must 
be  supplied  by  some  sort  of  a  lubricator  which  gradually  delivers 
oil  to  the  motor. 

The  amount  of  oil  required  per  stroke  of  the  piston  of  a  motor 
is  in  a  measure  proportional  to  the  rate  at  which  the  motor  is 
working.  More  oil  is  required  for  a  heavy  load  than  for  a  light 


1/4  THE   GAS  ENGINE 

one  when  the  speed  of  the  motor  is  constant.  The  oil  required 
for  variable-speed  motors  is  approximately  proportional  to  both 
the  speed  and  the  load.  The  refinement  of  lubricating  in  propor- 
tion to  the  work  per  stroke  does  not  seem  to  have  been  attempted. 
It  is  doubtful  as  to  its  being  worth  while.  But  practically  all 
the  lubricators  for  variable-speed  motors,  except  the  simplest 
gravity  types,  supply  the  oil  more  or  less  nearly  in  proportion  to 
the  speed  of  rotation.  When  the  splash  system  is  used,  it  is 
not  so  important  that  the  rate  of  feed  of  the  oil  shall  be  pro- 
portional to  the  speed.  But  when  the  motor  works  steadily  on  a 
heavy  load  for  a  long  time,  the  rate  of  gravity  feed  that  is  suit- 
able for  a  light  load  is  not  rapid  enough  for  a  heavy  one. 

101.  Lubricators.  —  There  are  four  distinct  types  of  lubri- 
cators used  on  internal-combustion  motors,  as  classified  accord- 
ing to  the  method  of  delivering  the  oil.  They  are: 

Gravity  feed; 

Mechanical  oil  supply  and  gravity  delivery; 

Compression  feed; 

Positive  mechanical  feed. 

The  gravity-feed  lubricators  that  are  used  on  gas  and  oil 
motors  are  principally  of  the  adjustable  sight-feed  type.  The 
rate  of  flow  of  the  oil  is  adjusted  by  a  needle  or  cone-point  regu- 
lator, and  is  observed  through  the  glass  sight  below  the  point 
from  which  the  oil  drops.  The  gravity  lubricator  can  be  used 
where  there  is  no  compression  resistance  to  feed  against.  It 
can  be  used  for  the  crank  shaft  of  an  enclosed  crank  case,  four- 
cylinder  vertical  motor  of  the  usual  type  in  which  two  of  the 
pistons  move  upward  in  unison  while  the  other  two  move  down- 
ward, since  neither  compression  nor  partial  vacuum  is  produced 
in  this  form  of  motor. 

The  mechanical-supply  and  gravity-delivery  lubricator  was 
used  on  the  early  horizontal  motors  of  the  Otto  type  for  lubricating 
the  piston.  It  still  finds  considerable  application  to  this  style  of 
motor.  In  it  a  mechanically  driven  part,  generally  rotary,  dips 
into  a  reservoir  of  oil  and  carries  some  of  it  up  over  the  open 
end  of  a  tube  which  extends  down  through  the  cylinder  wall  to 


LUBRICATION  OF  MOTOR  175 

the  bore  of  the  cylinder.  Some  of  the  oil  either  drops  or  is  scraped 
off  the  rotating  part  as  it  passes  over  the  top  of  the  tube,  and  flows 
down  through  it  to  the  piston.  If  the  pressure  due  to  a  leaky 
piston  blows  the  oil  up  out  of  the  tube,  it  is  caught  in  the  cup  or 
reservoir  and  again  carried  up  by  the  rotating  part. 

In  several  forms  of  motor  with  an  enclosed  crank  case  the  air 
or  mixture  in  the  case  is  alternately  compressed  and  expanded. 
The  gravity-feed  lubricator  will  not  deliver  oil  into  the  com- 
pressed air. 

The  compression-feed  lubricator  is  applicable  to  such  motors. 
In  some  of  its  forms  a  pipe  connects  the  crank  case  with  the  air 
space  above  the  oil  in  the  lubricator  reservoir.  The  pipe  ter- 
minates in  a  check  valve  in  the  lubricator.  When  the  air  is 
compressed  in  the  crank  case,  some  of  it  is  forced  into  the  air 
space  of  the  lubricator  and  retained  there  under  pressure  by  the 
check  valve.  When  the  pressure  in  the  crank  case  falls  as  the 
pistons  recede,  the  compressed  air  in  the  lubricator  forces  the  oil 
out  through  the  openings  for  that  purpose.  The  oil  is  fed  out  and 
regulated  as  in  a  sight-feed  gravity  lubricator,  except  that  the 
orifice  can  be  at  or  above  the  level  of  the  oil  provided  it  is  con- 
nected with  the  body  of  the  oil  by  a  passage  that  opens  below  its 
surface.  If  the  compressed  air  is  not  released  from  the  lubricator 
when  the  motor  stops,  it  will  continue  to  feed  oil  out  till  the 
pressure  falls.  A  release  valve  is  generally  provided.  It  is 
opened  by  a  pressure  of  the  finger  when  the  motor  is  stopped. 

Some  of  the  types  of  single-acting  motors  in  which  the  air  is 
alternately  compressed  and  expanded  in  the  enclosed  crank  case 
are:  single-cylinder  motor;  two-cylinder  opposed  motor,  with  the 
cylinders  on  opposite  sides  of  the  crank  shaft  and  the  cranks 
1 80  degrees  apart,  so  that  the  pistons  alternately  approach  and 
recede  from  each  other;  two-cylinder,  twin-cylinder  motors,  in 
which  the  cylinders  are  side  by  side  and  the  pistons  move  in 
unison  toward  and  away  from  the  crank  shaft. 

The  positive-feed  lubricator  in  one  of  its  forms  has  a  number 
of  small  plungers  and  corresponding  cylinders  or  pipe  ends,  one 
for  each  outlet  of  the  lubricator.  The  lower  ends  of  the  plungers 
and  the  cylinders  are  submerged  in  the  reservoir  of  oil.  The 


1/6  THE  GAS  ENGINE 

plungers  are  consecutively  lifted  by  a  rotating  part,  and  oil  flows 
into  the  cylinder  beneath  the  plunger  through  a  small  hole  in  the 
side  of  the  oil  cylinder.  The  plunger  is  then  released  and  a 
spring  snaps  it  down  suddenly.  The  side  orifice  of  the  cylinder 
is  closed  as  the  plunger  passes  it.  The  descent  of  the  plunger 
forces  the  oil  into  a  tube  which  carries  it  to  the  part  to  be  lubri- 
cated. There  are  no  valves  in  the  device  for  forcing  the  oil  out. 
The  plunger-lifting  part  of  the  lubricator  is  driven  by  the  motor 
at  a  speed  proportional  to  that  of  the  motor.  The  amount  of  oil 
fed  to  the  motor  is  therefore  approximately  proportional  to  the 
speed  of  rotation  of  the  motor. 

Practically  all  mechanically  driven  lubricators  deliver  oil  at  a 
rate  approximately  proportional  to  the  speed  of  the  motor. 

Slow-moving  mechanically  driven  plunger  pumps  with  valves 
are  used  in  some  of  the  other  positive-feed  lubricators. 


CHAPTER  VII. 
DISPOSAL   OF  EXHAUST   GASES. 

102.  Precautions.  —  Since  the  exhaust  gases  from  an  internal- 
combustion  motor  are  hot,  and  since  combustible  mixture  may 
be  mingled  with  them  at  times,  the  pipes  or  passages  through 
which  the  exhaust  is  carried  to  the  atmosphere  must  be  so  located 
and  protected  as  not  to  injure  anything  by  their  heat,  and  must 
be  strong  enough  to  resist  the  pressure  of  explosions  in  them.     It 
is  often  desirable  to  carry  the  exhaust  from  a  small  stationary 
motor  out  through  a  chimney  or  flue  of  a  building  in  which  the 
motor  is  located.     In  such  a  case  the  exhaust  pipe  must  be 
extended  the  full  length  of  the  flue   so  that  the  gases  will  be 
discharged  directly  into  the  atmosphere.     If  the  exhaust  is  dis- 
charged into  the  masonry  flue  and  an  explosion  occurs  in  it,  the 
flue  is  apt  to  be  wrecked. 

The  discharge  of  a  spray  of  water,  as  cooling-jacket  water, 
into  the  exhaust  pipe  reduces  its  temperature  and  lessens  the 
liability  of  explosions.  This  is  not  generally  practiced  for 
stationary  motors  of  small  size,  however.  If  there  is  much 
sulphur  dioxide  (SO2)  in  the  exhaust  gases,  cooling  with  water 
causes  destruction  of  metal  pipes  by  chemical  action. 

The  exhaust  should  never  be  discharged  into  a  room  even  for  a 
short  time.  A  small  quantity  of  the  gases  will  cause  headache, 
and  a  large  quantity  asphyxiation.  There  is  no  warning  odor, 
and  fainting  is  apt  to  occur  before  the  danger  is  realized. 

When  too  rich  a  mixture  is  used  in  a  gasoline  motor,  the  exhaust 
gases  will  also  cause  the  eyes  to  suffer  by  smarting  and  pain. 

The  danger  is  greatest  in  heavy,  damp  weather. 

103.  Silencing  the  Exhaust.  —  The  pressure  of  the  gases  in 
the  cylinder  of  an  internal-combustion  motor  is  still  high  enough 
when  the  exhaust  valve  opens  to  cause  them  to  escape  with  a 
loud  explosive  sound,  except  in  compound  motors  or  others  of 

177 


1/8  THE  GAS  ENGINE 

unusual  design  in  which  the  expansion  is  carried  out  to  almost 
atmospheric  pressure.  Some  provision  is  generally  made  for 
deadening  or  silencing  the  sound  of  the  exhaust.  The  apparatus 
for  this  purpose  is  generally  known  as  a  silencer  or  muffler. 

An  efficient  muffler  not  only  deadens  the  noise  of  the  exhaust, 
but  also  offers  a  minimum  resistance  to  the  escape  of  the  gases. 
Any  resistance  to  the  escape  of  these  gases  causes  a  back  pressure 
against  the  piston  of  the  motor  during  the  exhaust  stroke,  or 
against  the  piston  of  the  pump  that  forces  in  the  new  charge  in 
two-cycle  motors,  and  thus  reduces  the  efficiency  of  the  motor  and 
decreases  the  amount  of  power  that  it  will  develop. 

104.  Subterranean    Mufflers    or    Silencers.  —  For    stationary 
motors,  the  exhaust  is  generally  discharged  into  a  buried  tank 
or  a  pit  when  ground  space  is  available.     The  gas  expands  to  a 
low  pressure  in  the  receptacle  and  then  escapes  to  the  atmos- 
phere through  a  comparatively  small  pipe  or  opening. 

For  very  large  motors  a  pit  or  well  is  generally  excavated  and 
used  in  the  manner  just  described. 

The  noise  is  more  completely  deadened  by  filling  the  well  with 
loose  broken  stone,  coarse  cinders,  slag,  etc. 

Since  some  of  the  combustible  mixture  is  apt  to  pass  through 
the  motor  at  times  and  on  into  the  mufHer,  and  may  be  exploded 
there  by  the  hot  gases  of  a  subsequent  discharge,  the  muffler 
should  be  provided  with  means  of  relieving  the  pressure  of  the 
explosion  instantly,  so  that  it  may  not  be  blown  to  pieces.  A 
hinged  trap  door  of  planks  answers  this  purpose  well  for  large 
pits,  and  a  large  short  pipe  extending  from  the  barrel  or  tank 
to  the  atmosphere  and  closed  by  a  relief  valve  at  the  top  is 
suitable  for  smaller  sizes.  The  pipe  from  the  motor  to  the 
muffler  should  be  strong  enough  to  resist  the  pressure  of  these 
explosions. 

105.  Exposed  Muffler. — When  the  muffler  is  not  buried,  it 
is  made  of  metal  strong  enough  to  resist  the  pressure  of  explo- 
sions in  it.     If  the  exhaust  pipe  from  the  motor  to  the  muffler  is 
long,  there  should  be  a  relief  valve  either  on  the  muffler  or  very 
near  it. 

The  exposed  metal  muffler  has  either  a  comparatively  large 


DISPOSAL  OF  EXHAUST  GASES  179 

chamber,  or  a  number  of  chambers,  into  which  tthe  exhaust  gas 
is  discharged  and  expanded  and  then  passes  out  to  the  atmos- 
phere. When  the  volume  of  the  muffler  is  large  in  proportion 
to  the  size  of  the  exhaust  pipe,  the  escape  from  the  muffler  is 
often  made  through  a  single  large  pipe  into  the  atmosphere. 
But  if  the  muffler  is  small,  the  discharge  is  made  through  a  great 
number  of  small  orifices  direct  into  the  atmosphere. 

One  simple  form  of  muffler  consists  of  two  comparatively 
small  enlargements  of  the  exhaust  pipe  in  series  and  a  short 
distance  apart  in  the  pipe.  The  gas  expands  in  the  first  one 
and  then  passes  through  the  pipe  between  them  into  the  second 
for  further  expansion  and  then  escapes  through  a  length  of  pipe 
to  the  atmosphere. 

Another  form  of  muffler  has  two  or  more  pipes  of  different 
diameter  concentrically  arranged  in  a  nest,  and  the  ends  of  all 
the  pipes  are  closed  by  one  pair  of  heads.  The  exhaust  is 
received  inside  the  smallest  pipe  and  passes  from  it  through  a 
number  of  small  holes  into  the  next  larger  pipe,  and  so  on  to 
the  outer  tube  or  casing,  and  thence  to  the  atmosphere  direct  or 
through  a  pipe  extension. 

Still  another  form  is  made  up  of  a  number  of  thin  metal  disks 
slightly  concaved  and  placed  on  a  pipe  so  that  the  convex  side  of 
the  first  disk  forms  one  end  of  the  muffler  and  the  concave  side 
of  the  second  disk  is  placed  toward  that  of  the  first  one  so  that 
the  outer  edges  of  the  two  press  together.  The  convex  side  of 
the  third  disk  is  placed  next  to  that  of  the  second  one  and 
presses  against  it  at  the  edge  of  the  central  hole,  and  so  on  for  all 
the  disks.  The  pipe  through  the  disk  is  stopped  at  one  end 
and  has  holes  communicating  with  the  spaces  between  the 
concave  sides  of  the  disks.  The  exhaust  gases  pass  from 
the  pipe  through  the  holes  into  the  enclosed  spaces  between  the 
disks  and  escape  through  the  cracks  between  their  outer  edges. 

1 06.  Submerged  Exhaust  Pipe.  —  On  launches  it  is  quite 
common  practice  to  submerge  the  end  of  the  exhaust  pipe  in  the 
sea  water.  When  this  is  done,  the  precaution  should  be  taken 
to  give  the  pipe  sufficient  fall  to  prevent  drawing  the  water  up 
into  the  motor  by  the  contraction  of  the  hot  gases  in  the  pipe 


180  THE   GAS  ENGINE 

when  the  motor  is  stopped,  or  after  an  explosion  in  the  exhaust 
pipe.  A  check  valve  is  often  used  to  meet  this  and  other  con- 
tingencies tending  toward  the  same  result. 

107.  Muffler  Cut-Out.  —  A  cut-out  or  relief  valve  is  commonly 
used  on   automobiles.     It   is  controlled  by  the  driver,   and   is 
opened  when  the  maximum  power  that  the  motor  will  develop 
is  desired,  as  when  climbing  a  grade  or  speeding  up  quickly. 

1 08.  Momentary  Back  Pressure.  —  In  a  four-cylinder,  four- 
cycle motor  whose  impulses  occur  at  equal  time  intervals  and 
whose  valves  have  the  usual  setting,  the  exhaust  valve  of  one 
combustion  chamber  opens  before  the  completion  of  the  exhaust 
stroke  of  the  piston  of  one  of  the  other  cylinders.     If  the  exhaust 
pipes  from  the  two  combustion  chambers  (or  from  all  of  them) 
are  brought  together  into  a  single  main  passage  near  the  motor, 
this  action  of  the  exhaust  will  produce  a  momentary  increase  of 
pressure  in  the  latter  combustion  chamber  unless  the  connections 
between  the  single  exhaust  pipes  and  the  main  pipe  are  cor- 
rectly made.     This  increase  of  pressure  usually  occurs  during 
the  early  part  of  the  suction  stroke  of  the  piston  and  before  the 
inlet  valve  of  the  combustion  chamber  affected  is  opened.     While 
the  action  of  the  momentary  back  pressure  on  the  piston  is  not 
directly  harmful  in  affecting  the  power  of  the  motor,  it  does  act 
to  reduce  the  amount  of  charge  that  is  drawn  into  the  cylinder. 
This  is  because  the  exhaust  valve  closes  while  there  is  momen- 
tary back  pressure  in  the  cylinder  and  thus  retains  more  inert 
gases  of  combustion  than  would  be  retained  at  atmospheric 
pressure  in  the  cylinder. 

The  proper  method  of  connecting  the  individual  exhaust 
pipes  to  the  main  is  to  bring  them  nearly  parallel  with  the  latter 
where  they  are  connected,  so  that  the  Y  formed  will  have  a  very 
sharp  angle  between  the  branches.  The  discharge  from  one 
combustion  chamber  will  then  have  a  tendency  to  draw  the  ex- 
haust gases  from  the  others  by  ejector  action  instead  of  pro- 
ducing a  back  pressure  as  when  the  passages  are  at  right  angles 
to  each  other  at  their  connection. 


CHAPTER   VIII. 
STARTING  AND  ADJUSTING  THE  MOTOR. 

109.  Methods  of  Starting  the  Motor.  —  There  are  three 
methods  in  general  use  for  starting  an  internal-combustion 
motor.  They  are: 

1.  Rotating  the   motor  by   external   power  till   a   charge   is 
exploded  in  the  usual  manner  and  the  motor  then  runs  itself. 
Small  motors  are  "cranked"  or  otherwise  turned  by  hand,  and 
large  ones  are  driven  from  some  source  of  mechanical  power. 

2.  Starting  the  motor  from  rest  by  its  own  impulse.     This  is 
generally  done  by  exploding  a  charge  of  the  combustible  mixture 
in  the  cylinder.     An  impulse  is  thus  given  the  piston  in  much 
the  same  manner  as  when  the  motor  is  running,  so  that  it  starts. 
A  less  common  method,  although  probably  older,  is  to  fire  a 
charge  of  gunpowder  in  the  cylinder. 

3.  Driving  by  compressed  air  passed  into  the  cylinder  to  act 
on  the  piston  in  a  manner  similar  to  that  of  steam  in  steam 
engines. 

no.  Relieving  the  Compression  while  Starting. — The  larger 
sizes  of  motors  intended  to  be  started  by  hand  are  often  con- 
structed so  that  the  compression  can  be  cut  down  to  a  much 
lower  pressure  for  starting  than  is  used  during  the  regular  oper- 
ation of  the  motor.  A  very  common  method  of  doing  this  is  to 
have  the  Tegular  cams  move  aside  so  as  to  bring  the  starting  cams 
into  position  for  actuating  the  motor  valves-.  The  starting  cams 
hold  either  the  inlet  valve  or  the  exhaust  valve  of  each  cylinder 
open  during  a  portion  of  the  compression  stroke,  so  that  part  of 
the  charge  that  was  drawn  in  during  the  preceding  suction 
stroke,  in  a  four-cycle  motor,  is  either  forced  back  through  the 
inlet  port  or  out  through  the  exhaust  port.  When  the  inlet 
valve  is  mechanically  operated,  the  starting  cam  is  applied  to  it, 
but  with  an  automatic  inlet  valve  the  starting  cam  can  act  only 

181 


1 82  THE  GAS  ENGINE 

on  the  exhaust  valve.  The  latter  has  the  seriously  objectionable 
feature  of  passing  combustible  mixture  through  the  motor  into 
the  exhaust  pipe,  and  of  the  resulting  danger  of  explosions  in 
the  exhaust  pipe  and  muffler. 

In  automobile  motors  the  cam  shaft  is  shifted  to  the  starting 
position  by  putting  on  the  starting  crank.  The  throwing  of  the 
hand  crank  out  of  engagement  when  the  motor  starts  on  its  own 
impulses  allows  the  cam  shaft  to  come  back  to  the  running 
position.  Some  of  the  large  motors  that  are  started  by  external 
mechanical  power  are  provided  with  means  for  relieving  the 
compression  in  the  same  general  way  as  the  small  ones. 

in.  The  preparations  for  starting  a  motor  are  practically  the 
same  to  a  certain  extent,  whatever  the  method  of  starting.     The 
general  preparations   which   are  given   immediately  below   do 
not  all  apply  to  any  one  motor,  but  such  of  them  as  do  apply  to 
any  particular  case  should  be  made.     It  should  be  seen  that : 
Fuel  is  in  the  tank  for  motors  that  use  liquid  fuel; 
The  vent  of  the  gravity  fuel  tank  is  not  clogged; 
The  compression  fuel  tank  is  tightly  closed; 
Gas  is  in  the  supply  pipe  for  motors  using  permanent  gas. 
This  can  be  done  by  lighting  a  jet  or  burner  connected 
to  the  pipe  at  a  point  near  the  motor; 
Lubricating  oil  is  in  all  the  lubricators; 
The  reservoir  of  a  compression  lubricator  is  tightly  closed; 
Grease  cups  are  filled; 

Cooling  water  is  provided.  If  a  stationary  motor  is  located 
in  a.  warm  room  and  the  cooling  water  is  very  cold,  as 
when  it  flows  from  mains  or  an  exposed  tank  in  winter, 
it  may  be  advisable  to  start  the  motor  before  turning  on 
the  cooling  water.  This  applies  especially  to  gasoline, 
naphtha,  and  alcohol  motors. 
Then: 

Give  the  grease  cups  a  turn  to  force  grease  into  the  bearings ; 
Turn  on  the  lubricating  oil; 

Disengage  the  clutch  when  one  is  used  between  the  motor 
and  a  load  having  considerable  inertia  or  a  load  that 
must  be  started  slowly. 


STARTING  AND  ADJUSTING  THE  MOTOR  183 

The  operations  following  these  depend  so  much  on  the  kind 
of  motor  and  the  method  of  starting  that  they  must  be  differen- 
tiated. 

Starting  by  External  Power. 

112.  Starting  a  Small  Electrically  Ignited  Gas  Motor  by  Crank- 
ing. —  After  such  of  the  above  preparations  as  apply  to  the 
motor  have  been  made: 

Set  the  igniter  in  the  late  or  retard  position ; 

Set  the  relief  cam  mechanism  so  that  the  compression  will 
be  cut  down  when  starting; 

Turn  on  the  gas,  but  only  part  way  if  there  is  no  fuel  valve 
to  prevent  its  flow  from  pressure  pipes  into  the  air  passage 
or  mixing  chamber; 

Crank  the  motor.  Always  pull  up  on  the  crank.  The 
cranking  should  be  done  immediately  after  the  gas  is 
turned  on  if  there  is  no  provision  to  prevent  flow  of  the 
gas  into  the  air  passage  or  mixture  chamber; 

As  soon  as  the  motor  begins  to  run  itself: 

Turn  on  the  cooling  water  if  it  has  not  been  done  before 
(see  preparations).  This  is  not  necessary  in  a  circu- 
lating system; 

Close  the  throttle  enough  to  prevent  racing  if  the  motor  is 
hand  controlled; 

Open  the  gas  valve  to  its  proper  setting  (see  below); 

Advance  the  ignition  (see  below). 

There  is  no  provision  for  retarding  the  time  of  ignition  in  many 
small  stationary  motors.  Under  such  conditions  it  is  safer  to 
open  a  switch  in  the  primary  circuit  of  the  ignition  system  before 
cranking  the  motor.  Then  crank  up  to  a  fair  speed  and  close 
the  switch.  If  this  precaution  is  not  taken,  the  motor  may  start 
backward  (kick)  if  the  ignition  comes  as  early  as  it  should  for 
economical  operation  at  fairly  high  speed.  When  provision  is 
made  for  retarding  the  ignition  in  a  small  stationary  motor,  there 


1 84  THE  GAS  ENGINE 

are  often  only  two  positions  in  which  the  timer  or  igniter  can  be 
set  —  a  starting  and  a  running  position. 

If  an  electric  generator  that  does  not  give  enough  pressure  or 
current  to  cause  ignition  until  the  motor  has  been  cranked  up  to 
high  speed,  is  used,  there  is  no  necessity  for  the  precaution  of 
breaking  the  ignition  circuit  when  starting. 

The  amount  of  opening  to  be  given  the  hand-opened  gas  valve 
depends  on  the  pressure  of  the  gas  and  its  richness  or  heat  value. 
The  opening  that  gives  maximum  power  can  be  determined  by 
noting  the  load  that  the  motor  will  pull.  The  setting  for  maxi- 
mum power  does  riot  generally  correspond  to  that  for  maximum 
economy  of  fuel,  however.  The  economy  of  fuel  is  generally 
better  with  slightly  less  gas  than  is  required  for  maximum  power. 

The  hand  crank  for  starting  the  motor  should  be  made  so  as  to 
free  itself  and  cease  to  rotate  with  the  motor  as  soon  as  the  latter 
starts  on  its  own  power. 

For  the  greatest  safety  to  the  operator,  the  hand  crank  should 
be  made,  when  possible,  so  that  it  can  be  pulled  only  upward  at 
the  time  of  ignition.  Then,  if  the  motor  kicks,  the  crank  may 
be  snapped  or  jerked  out  of  one's  hand  with  less  danger  than 
when  pressing  down  on  it. 

113.  Starting  an  Electrically  Ignited  Stationary  Gasoline 
Motor  by  Cranking.  —  (See  preparations. ) 

Turn  on  the  gasoline  and  lubricating  oil; 

Set  the  timer  or  igniter  for  late  ignition; 

Close  the  throttle  well  toward  shut  so  that  the  motor  will 

not  race  if  hand  controlled; 

Prime  the  carbureter  (this  is  not  generally  necessary); 
Crank  the  motor;  pull  up  on  the  crank; 
Turn  on  the  cooling  water  if  it  has  not  been  done  before 

(see  preparations); 
Advance  the  timer  and  close  the  throttle  still  further  if  the 

motor  is  to  run  light  for  a  while. 

See  preceding  section  regarding  timer  and  crank. 
It  sometimes  happens  that  the  slow  speed  of  cranking  does 
not  cause  enough  gasoline  to  mix  with  the   air  while  cranking 


STARTING  AND  ADJUSTING  THE  MOTOR  185 

to  form  a  combustible  mixture.  The  priming  o^  the  carbureter 
is  intended  to  remove  this  difficulty.  If  there  is  no  way  of 
priming  the  carbureter,  its  air  intake  may  be  partly  closed 
with  one's  hand  or  anything  else  that  is  convenient,  while 
cranking.  This  causes  enough  suction  to  draw  out  sufficient 
gasoline. 

When  the  motor  is  very  cold,  as  one  that  has  been  exposed  to 
freezing  weather,  it  is  sometimes  very  difficult  to  get  the  fuel, 
especially  if  it  is  of  a  poor  grade  for  the  purpose,  to  vaporize. 
Most  motors  are  provided  with  a  small  valve  or  pet -cock  at  the 
top  of  the  cylinder,  through  which  gasoline  can  be  poured  into 
the  cylinder.  If  a  small  quantity  of  gasoline  is  poured  in  and 
left  for  a  minute  or^two,  it  will  generally  vaporize  and  diffuse 
enough  to  produce  a  mixture  that  will  ignite. 

A  still  further  expedient  with  a  cold  motor  is  to  pour  hot  water 
into  the  jacket  space,  or  into  the  circulating  system  at  a  con- 
venient place.  In  the  latter  case,  a  motor  with  a  circulating 
pump  should  be  rotated  by  hand  to  force  the  water  into  the 
jacket. 

Still  another  expedient,  which  should  be  that  of  last  resort,  is 
to  heat  the  cylinder  and  inlet  pipe  with  a  torch,  or  by  putting  a 
little  gasoline  on  them  and  burning  it  off.  Very  little  gasoline 
should  be  put  on  at  first,  and  then  more  can  be  squirted  on  from 
an  oil  can  with  a  small  opening  in  the  nozzle.  The  gasoline  will 
not  ignite  in  the  can,  for  the  flame  cannot  pass  in  through  the 
small  opening. 

114.  Starting  a  Large,  Electrically  Ignited  Gas  Motor  by 
External  Mechanical  Power.  —  The  method  is  practically  the 
same  as  for  the  small  gas  motor,  except  the  substitution  of  mechan- 
ical power  for  muscular  effort. 

The  gas  motor  to  be  started  may  be  driven  by  friction  gears 
pressing  against  the  flywheel.  In  such  a  device  the  driving  gear 
should  be  movable  so  as  to  be  withdrawn  from  engagement  with 
the  flywheel  when  the  motor  starts  on  its  own  power. 


1 86  THE  GAS  ENGINE 

Starting  the  Motor  by  Its  Own  Impulse. 

115.  A  single-cylinder,  single-acting  gas  motor  with  electric 
ignition  can  be  started  by  its  own  impulse  in  the  following  manner 
after  it  has  been  stopped  by  cutting  off  the  fuel  supply:  Set  the 
crank  past  its  dead-center  position  with  the  piston  a  short  distance 
out  on  its  impulse  stroke.  The  crank  may  be  set  as  much  as 
30  degrees  or  even  more  past  dead  center. 

Open  the  hand  valve  and  allow  gas  to  flow  into  the  combustion 
space  through  a  small  auxiliary  pipe  or  opening  for  this  purpose. 
The  gas  mixes  with  the  air  in  the  cylinder  that  was  drawn  in  after 
the  fuel  was  cut  off.  After  enough  gas  has  passed  in  to  make  a 
combustible  mixture,  as  determined  by  judgment  or  a  small  gas 
meter,  its  flow  is  to  be  cut  off.  Then  after  the  suitable  prepara- 
tions (see  preparations)  have  been  made,  the  charge  is  to  be 
ignited.  This  will  give  the  piston  an  impulse  sufficient  to  drive 
the  motor  till  a  charge  is  drawn  in  and  ignited. 

When  a  battery  is  used  in  connection  with  an  induction  coil 
for  ignition,  the  first  ignitioij  can  be  made  by  leaving  the  battery 
circuit  open  till  the  time  to  ignite  and  then  closing  it.  The  jump 
spark  thus  produced  will  ignite  the  charge. 

If  an  oscillating-armature  magneto  is  used,  the  electric  spark 
or  arc  can  be  produced  by  snapping  the  armature  over  by  hand. 
In  the  absence  of  an  ignition  system  suitable  to  cause  ignition 
when  the  motor  is  at  rest,  one  manufacturer  has  adopted  the 
expedient  of  striking  a  match  inside  the  combustion  chamber 
to  ignite  the  charge.  The  end  of  a  match  is  fastened  in  the 
plunger  point  of  a  holder  and  the  latter  screwed  into  a  threaded 
hole  in  the  combustion  chamber  wall.  The  plunger  is  then 
forced  in  and  the  match  ignited  by  rubbing  against  a  surface 
provided  for  the  purpose.  The  flame  of  the  match  ignites  the 
charge. 

116.  Starting  the  Motor  on  "  Compression."  —  If  the  ignition 
is  cut  out  to  stop  a  four-cycle,  single-acting,  four-cylinder  motor, 
and  the  throttle  is  opened  during  the  last  revolutions  before 
stopping,  at  least  two  of  the  cylinders  will  contain  a  combustible 
charge  when  the  motor  stops.  The  piston  of  one  of  the  charged 


STARTING  AND  ADJUSTING  THE  MOTOR 


187 


cylinders  will  stop  'on  the  impulse-stroke  position.  The  motor 
can  be  started  again  by  exploding  the  charge  in  this  cylinder. 
In  a  hand-controlled  motor  the  ignition  can  be  effected  by  mov- 
ing the  timer  to  the  position  that  will  give  a  spark  in  the  cylinder 
whose  impulse  will  start  the  crank  in  the  right  direction,  that  is, 
in  the  cylinder  whose  piston  is  part  way  out  on  the  impulse 
stroke. 

Two-cylinder,  single-acting,  four-cycle  motors  will  some- 
times stop  in  position  to  be  started  on  compression,  but  this  is 
unusual  and  in  the  nature  of  an  accident.  Motors  with  more 
than  two  cylinders  generally  stop  so  as  to  start  on  compression, 
provided  the  fuel  has  free  access  and  is  not  exploded  while  stop- 
ping. 


FIG.  76. 
Starting  Valve  for  Starting  Motor  with  Compressed  Air. 

1.  Motor  cylinder.  3.    Coil  spring  to  hold  valve  closed. 

2.  Valve.  4.    Lever  for  opening  valve. 

5.    Connection  to  compressed  air  supply. 

The  motor  is  put  into  position  with  the  piston  a  short  distance  out  on  the  impulse 
stroke  and  then  the  compressed  air  is  admitted  by  opening  the  valve  2  by  means 
of  the  hand  lever  4. 

The  length  of  time  that  a  motor  will  retain  a  charge  in  the 
cylinder  so  as  to  start  on  compression  depends  on  the  tightness 
of  the  cylinder,  piston,  valves,  etc.  The  writer  has  frequently 


1 88  THE   GAS  ENGINE 

seen  motors  that  have  been  in  considerable  service  started  in  this 
manner  after  standing  for  a  week. 

117.  Starting  by  Firing  a  Blank  Cartridge  in  the  Cylinder.  — 
Motors  are  not  infrequently,  and  with  entire  success,  started  in 
this  manner.     The  powder  should  be  comparatively  slow  burn- 
ing, as  black  gunpowder.     A  blank  cartridge,  such  as  is  used  in 
a  gun,  is  suitable.     The  amount  of  powder  necessary  depends 
on  the  size  of  the  motor,  of  course.     About  four  drams,  or  120 
grains,  should  start  a  motor  with  a  cylinder  bore  six  inches  in 
diameter. 

It  is  advisable  to  begin  with  small  charges  of  powder  and  grad- 
ually increase  the  amount  until  it  is  great  enough. 

Suitable  means  of  holding  the  cartridge,  as  a  breech  block, 
must  of  course  be  provided.  The  piston  of  the  cylinder  in  which 
the  cartridge  is  fired  should  be  placed  a  short  distance  out  on  its 
impulse  stroke,  with  the  crank  for  that  cylinder  some  distance 
past  the  dead-center  position. 

1 1 8.  Stresses  Due  to  Starting  a  Motor  by  Its  Own  Impulse.  - 
The  explosion  of  a  charge  of  combustible  gas  or  a  cartridge  in 
the  cylinder  when  the  motor  is  at  rest  produces  a  higher  pressure 
in  the  cylinder  than  if  the  piston  were  moving  out  on  its  impulse 
stroke.     The  force  transmitted  to  the  crank  shaft  is  greater  in 
proportion  to  the  pressure  against  the  face  of  the  piston  than 
when  the  speed  of  the  piston  is  accelerating  rapidly  at  the  time 
of  explosion,  as  is  the  case  when  the  motor  is  running  and  the 
charge  is  fired  at  the  usual  time  at  about  the  beginning  of  the 
impulse  stroke.     It  .is  therefore  not  advisable  to  explode  a  full 
charge  in  the  cylinder  when  the  motor  is  at  rest,  on  account  of 
the  great  stresses  that  such  an  explosion  would  produce,  unless 
the  motor  is  constructed  with  a  view  to  starting  it  with  full 
charges.     The   practice   of   starting   in   this   manner   is   mostly 
confined  to  motors  below  medium  size. 

Starting  on  compression  does  not  produce  higher  pressure  in 
the  cylinder  than  the  explosions  during  regular  running,  for  the 
piston  stops  in  such  a  position  that  the  charge  is  but  slightly 
compressed  when  ignited.  The  pressure  of  explosion  is  higher, 
the  higher  the  compression  pressure  at  the  time  of  igniting. 


STARTING  AND  ADJUSTING  THE  MOTOR  189 

Starting  the  Motor  with  Compressed  Air* 

119.  The  use  of  compressed  air  in  the  cylinder  for  starting 
the  motor  is  a  certain  and  gentle  way.     It  is  much  used  on  large- 
size  motors.     The  cost  of  the  equipment  for  compressing  the  air 
is  an  objection  to  this  method  for  small  and  medium  size  motors, 
but  when  the  compressed  air  is  to  be  used  for  other  purposes  also, 
this  objection  disappears. 

120.  In    starting    a    single-cylinder,    single-acting   motor   by 
compressed  air,  the  usual  practice  is  to  use  a  hand  valve  to 
admit  the  compressed  air  to  the  cylinder  after  the  crank  shaft 
has  been  rotated  (barred  over)  to  bring  the  piston  to  a  position 
a  little  way  out  on  the  impulse  stroke.     The  compressed  air  is 
turned  on  and  quickly  shut  off  again  before  the  completion  of 
the  impulse  stroke.     The  momentum  given  the  moving  parts  in 
this  manner  is  sufficient  to  keep  them  moving  until  a  charge 
is   drawn  in  and  exploded  immediately  after  the  first  suction 
stroke. 

The  air  is  generally  compressed  by  a  compressor  driven  by 
the  motor  long  enough  to  store  up  a  sufficient  amount  of  the 
compressed  air  in  storage  tanks.  Some  attempts  were  made  in 
the  earlier  single-acting,  single-cylinder  motors  to  have  them 
act  as  air  compressors  while  stopping  after  the  fuel  was  cut  off. 
This  practice  has  not  come  into  much  use. 

121.  Starting  a  Motor  with  More  than  One  Combustion  Cham- 
ber by  Compressed  Air.  —  When  the  motor  has  more  than  one 
combustion  chamber,  compressed  air  can  be  used  in  one  of  them 
for  driving  the  motor  till  the   explosion  impulses  in  the  other 
combustion  chamber    (or  chambers)   come  into  effect  to  drive 
the  motor.     The  compressed  air  is  then  shut  off  and  the  motor 
operates  in  the  usual  manner. 

A  starting  valve-mechanism  must  be  brought  into  operation 
on  the  valves  of  the  combustion  chamber  to  which  the  compressed 
air  is  admitted,  so  as  to  cause  the  admission  valve  to  open  during 
the  early  part  of  each  outstroke  of  the  piston  and  the  exhaust 
valve  to  open  during  each  return  or  instroke  of  the  same  piston. 
*  See  also  Diesel  motor. 


190  THE   GAS  ENGINE 

The  starting  cams  or  other  starting  mechanisms  are  usually  made 
so  as  to  be  readily  moved  into  position  for  starting  and  promptly 
withdrawn  when  the  motor  has  gained  speed. 

An  automatic  device  for  cutting  off  the  compressed  air  is 
used  in  general  practice. 

Adjusting  the  Lubricator  and  Cooling  Water. 

122.  Lubricator  Adjustment.  —  The  lubrication  of  the  piston 
requires  more  care  than  that  of  the  other  parts  of  the  motor, 
although  it  is  very  important  that  all  of  the  bearings  shall  have 
plenty  of  oil  or  grease.  It  is  practically  impossible  to  give  the 
bearings  of  the  crank  shaft,  connecting  rod,  cam  shaft,  and  other 
similar  parts  too  much  oil,  but  an  excess  of  oil  for  the  piston  is 
accompanied  with  undesirable  results,  which  are  not  so  serious, 
however,  as  those  of  too  little  oil. 

The  piston  (or  cylinder)  lubricator  can  be  well  opened  at  first, 
so  that  blue  smoke  is  discharged  with  the  exhaust  gases,  and  then 
gradually  closed  just  enough  to  prevent  the  appearance  of  the 
blue  smoke.  The  oil  should  be  cut  down  slightly  and  the  motor 
allowed  to  run  at  least  several  minutes  before  making  further 
adjustment  of  the  piston  lubricator.  The  black  smoke  of  too 
rich  a  mixture  should  not  be  mistaken  for  the  blue  smoke  of  too 
much  oil.  The  actual  amount  of  piston-lubricating  oil  cannot  be 
well  specified  for  motors  in  general,  but  it  is  safe  to  start  with 
twenty  small  drops  a  minute  for  a  piston  5  inches  in  diameter  and 
running  at  high  speed.  The  condition  of  the  exhaust  gases  can 
be  observed  by  opening  a  small  hole  in  the  pipe  near  the  motor, 
or  by  partly  disconnecting  a  pipe  joint,  when  the  motor  dis- 
charges into  the  atmosphere  at  a  considerable,  or  unobservable, 
distance  from  the  motor,  as  is  frequently  the  case  with  stationary 
motors. 

For  the  bearings  of  small  motors  from  which  the  oil  is  allowed 
to  run  to  waste,  three  or  four  drops  a  minute  on  crank-shaft 
bearings  2  inches  in  diameter  and  running  at  400  to  500  revolutions 
per  minute  are  generally  sufficient.  The  smaller*  and  slower 
speed  cam  shaft  requires  but  very  little  oil. 


STARTING  AND  ADJUSTING  THE  MOTOR  191 

123.  Cooling- Water  Adjustment.  —  When  the,  cooling  water  is 
taken  from  water  mains  and  allowed  to  flow  to  waste  the  water 
valve  should  be  set  so  as  to  give  the  escaping  water  a  temperature 
as  near  the  boiling   point   as  possible.     The  amount  of  water 
depends  on  the  rate  at  which  the  motor  is  developing  power.     It 
requires  more  water  at  full  load  than  at  light  load.     Care  should 
be  taken  to  give  it  enough  water  for  the  heaviest  load  that  comes 
on  it. 

In  circulating  systems  of  cooling  there  is  seldom  any  means  of 
adjusting  the  rate  of  flow.  In  thermal  systems  the  water  in  the 
cooler  must  be  kept  above  the  opening  of  the  upper  pipe  from 
the  motor,  as  has  been  previously  stated. 

Adjusting  Spray  Carbureters  and  the  Ignition. 

124.  The  air-valve  stop,  not  generally  used,  is  not  referred  to 
in  the  following  direction  for  adjusting  carbureters.     This  stop 
is  used  in  some  carbureters  for  constant-speed  motors,  where  its 
function  is  to  positively  limit  the  lift  of  the  automatic  air  valve  of 
the  carbureter. 

It  should  be  remembered  that  the  more  the  lift  of  the  carbu- 
reter air  valve  is  restricted  by  the  stop,  the  richer  will  be  the 
mixture  when  the  motor  is  working  at  full  load.  The  intro- 
duction of  the  action  of  this  device  into  the  general  discussion 
would  make  it  complicated  to  an  extent  hardly  warrantable  on 
account  of  the  small  use  that  is  made  of  the  stop. 

125.  Rich  and  Lean  Fuel  Mixtures.  —  The  amount  of  power 
developed  by  a  motor  falls  off  from  the  maximum  with  either 
an  increase  or  a  decrease  in  the  proportion  of  the  fuel  in  the 
mixture,  and  the  charge  fails  to  ignite  when  it  becomes  either 
too  rich  or  very  lean.     If  the  mixture  is  very  rich,  but  still  ignites, 
black  smoke  will  be  discharged  with  the  exhaust.     The  exhaust 
from  an  over-rich  gasoline  mixture  has  a  strong   characteristic 
odor  and  is  painful  to  the  eyes,  even  if  it  is  not  so  rich  as  to  pro- 
duce black  smoke.     The  black  smoke  should  not  be  confused 
with  the  blue  smoke  that  comes  from  too  much  lubricating  oil 
in  the  cylinder  or  from  oil  of  the  wrong  quality. 


1 92  THE  GAS  ENGINE 

A  very  rich  combustible  mixture  burns  so  slowly  that  the  flame 
continues  long  enough  to  pass  out  into  the  exhaust  pipe  when 
the  exhaust  valve  (or  port)  is  opened.  This  heats  both  the 
cylinder  and  the  exhaust  valve  and  pipe  unduly,  as  well  as  wasting 
the  fuel.  The  ignition  of  an  over-rich  mixture  is  uncertain.  An 
unfired  charge  is  therefore  apt  to  pass  out  into  the  exhaust  pipe, 
where  it  is  subject  to  ignition  by  the  flame  of  a  succeeding  burn- 
ing charge  or  by  hot  particles  of  soot  in  the  exhaust  pipe  or 
muffler.  The  after  explosion,  or  muffler  explosion,  thus  pro- 
duced is  extremely  undesirable. 

Premature  ignition  is  apt  to  occur  with  the  continued  use  of 
too  rich  a  mixture,  on  account  of  the  carbon  or  soot  that  is  de- 
posited on  the  walls  of  the  combustion  chamber  while  the  charge 
is  burning.  This  deposit  becomes  ignited  and  burns  like  the 
soot  in  a  fireplace  in  a  house.  The  glowing  soot  ignites  the 
charge  prematurely,  generally  during  the  compression  stroke  of 
the  piston.  It  may,  however,  ignite  the  entering  mixture  during 
the  suction  stroke,  thus  causing  back  firing  into  the  intake  pipe. 

A  very  lean  mixture  is  also  slow  burning  and  uncertain  of 
ignition.  This  is  especially  true  when  the  charge  is  also  rare- 
fied by  a  nearly  closed  throttle.  The  characteristic  result  of  a 
lean  mixture  is  back  firing  into  the  inlet  pipe  and  carbureter,  or 
into  the  crank  case  of  a  two-cycle  motor  of  the  type  in  which  the 
mixture  is  compressed  in  the  crank  case.  The  back  firing  is 
caused  by  the  slow  burning  of  the  charge  till  the  fuel  port  is 
opened  and  the  mixture  in  the  inlet  passage  is  ignited  by  the 
flame  in  the  combustion  cuamber.  The  explosion  thus  pro- 
duced in  the  intake  passage  and  carbureter  is  sharp  and  light 
in  sound.  It  compares  with  an  exhaust  explosion  as  the  snap- 
ping of  a  percussion  cap  does  with  the  report  of  a  gun  using 
black  powder. 

Misfires  of  a  lean  mixture  are  also  conducive  to  explosions  in 
the  exhaust. 

When  the  fuel  mixture  is  too  rich  there  will  generally  be  com- 
bustible gas  carried  out  with  the  exhaust  in  the  form  of  carbon 
monoxide,  CO.  Carbon  monoxide  is  not  only  suffocating  but 
also  poisonous. 


STARTING  AND  ADJUSTING  THE  MOTOR  193 

The  following  method  of  detecting  CO  in  the,  exhaust  gases 
from  an  internal-combustion  motor  is  given  by  Mr.R.  E.Mathot.* 
"A  small  glass  flask,  about  two  inches  in  diameter  and  four 
inches  high,  closed  with  a  cork,  through  which  pass  two  vertical 
tubes,  is  used  for  collecting  some  of  the  exhaust  gas.  One  of 
the  tubes  is  connected  to  the  exhaust  pipe  of  the  engine,  while 
the  other  end  is  plunged  in  mercury  about  one  inch  deep  in  the 
flask.  As  soon  as  the  connection  between  the  exhaust  pipe  and 
flask  is  established,  some  of  the  exhaust  gas  will  be  blown  into 
the  flask  at  each  stroke,  and  the  mercury,  operating  as  a  check 
valve,  will  prevent  it  from  being  withdrawn.  The  air  contained 
in  the  flask,  and  afterward  the  exhaust  gas,  will  be  expelled 
through  the  second  pipe  open  to  the  atmosphere  and  ending 
inside,  at  the  top  of  the  flask. 

"To  detect  CO,  which  is  contained  in  the  exhaust  gas  con- 
tinuously rushing  through  the  flask,  a  small  piece  of  white 
blotting  paper  is  hung  in  the  flask,  the  paper  being  previously 
prepared  by  dipping  five  or  six  times  in  a  solution  of  double 
chlorid  of  palladium  and  sodium  of  such  concentration  as  to 
give  a  dark  brown  color,  and  drying  after  each  immersion. 

"If  there  is  more  than  1  per  cent  of  CO  in  the' exhaust  gases, 
the  paper  will,  in  two  or  three  minutes,  lose  its  bright  brown 
color  and  become  gray.  This  shows  insufficient  air  in  the  mix- 
ture for  combustion,  which  can  be  corrected  at  the  mixing 
valve." 

126.  Rough  Adjustments  for  Black  Smoke  and  Back-firing.  - 
If  black  smoke  (not  blue,  see  adjustment  of  lubricator)  is  dis- 
charged from  the  exhaust  after  the  motor  has  been  running  a 
minute  or  so  after  starting,  the  fuel  mixture  is  too  rich.  The  fuel 
valve  of  the  carbureter  should  be  closed  some,  or  the  air  valve  (of 
the  carbureter)  opened  more. 

If  the  motor  back-fires  with  a  sharp  explosion  in  the  intake  pipe 
and  carbureter,  it  may  be  due  to  having  the  throttle  nearly  closed 
and  the  ignition  set  late  in  a  hand-controlled  motor,  or  the  fuel 
mixture  may  be  too  lean.  Open  the  throttle  slightly  and  advance 
the  ignition  a  little.  If  this  does  not  stop  the  back  firing,  then, 

*  Trans.  Amer.  Soc.  Mechanical  Engineers,  April,  1908,  Vol.  30,  p.  401. 


IQ4  THE  GAS  ENGINE 

if  the  carbureter  has  been  previously  adjusted,  close  and  open  the 
needle  fuel  valve  quickly,  so  as  not  to  stop  the  motor,  bringing  the 
valve  back  to  the  same  setting  that  it  had.  This  will  generally 
remove  or  crush  foreign  matter  that  may  have  lodged  under  the 
valve.  If  the  back  firing  still  continues,  open  the  fuel  valve  still 
more,  or  close  the  air  valve  some.  Continue  this  till  black  smoke 
appears  at  the  exhaust  if  the  back  firing  does  not  stop  before.  If 
this  does  not  stop  the  back  firing,  it  is  probably  due  to  some  other 
cause  than  those  just  mentioned.  (See  back  firing). 

Closing  the  air  valve  enriches  the  mixture  in  greater  proportion 
with  a  closed  setting  of  the  throttle  and  slow  speed  of  the  motor 
than  with  an  open  throttle  and  high  motor  speed,  in  the  usual 
forms  of  carbureters.  The  same  effects  generally  obtain  when 
the  spring  is  adjusted  to  press  the  air  valve  harder  on  its  seat  in  a 
carbureter  with  a  spring-closed  air  valve.  Adjusting  the  spring 
to  press  the  air  valve  harder  on  its  seat  is  commonly  referred  to 
as  closing  the  air  valve. 

The  above  adjustments  are  only  rough  ones,  and  should  be 
followed  by  the  more  accurate  ones  described  later. 

127.  Adjusting  the   Carbureter  and   Ignition  on  a  Cut-Out- 
Governed   Motor.  —  (See    preceding    section    for   rough    initial 
adjustments.) 

Run  the  motor  on  a  constant  load  and  adjust  the  fuel  valve  and 
the  air  valve  to  obtain  the  maximum  number  of  cut-outs. 

Set  the  timer  to  give  earlier  and  later  ignition  till  the  position 
of  the  timer  that  gives  the  greatest  number  of  cut-outs  is  deter- 
mined. Leave  the  timer  in  this  position,  and 

Adjust  the  carbureter  again  as  at  first. 

Continue  the  adjustments  of  the  carbureter  and  timer  in  this 
manner  till  the  final  settings  for  the  greatest  number  of  cut-outs 
are  found. 

128.  Adjusting   the   Carbureter  and   Ignition   of  a  Throttle- 
Governed  Motor.  —  (See  rough  adjustments. )     To  make  the  best 
adjustment  for  regular  service,  the  motor  should  be  run  part  of 
the  time  on  a  nearly  full  load  of  constant  value  and  the  remainder 
of  the  time  on  a  small  constant  load  of  about  the  same  amount  as 
the  average  small  load  on  which  the  motor  is  to  operate.     These 


STARTING  AND  ADJUSTING  THE  MOTOR  195 

loads  can  be  obtained  by  the  use  of  an  absorption  dynamometer  if 
not  otherwise. 

The  object  in  each  case  is  to  secure  the  least  opening  of  the 
throttle  for  the  load  applied. 
Put  on  the  full  load : 

Set  the  air  valve  of  the  carbureter  at  about  mid-position; 
Adjust  the  fuel  valve  and  the  ignition  to  find  the  settings 

that  let  the  throttle  close  farthest. 
Put  on  the  small  load: 

Adjust  the  air  valve  to  give  the  least  opening  of  the  throttle; 
Set  the  air  valve  about  midway  between  its  first  and  second 

settings. 

Put  on  the  full  load  again  and  adjust  the  fuel  valve  and  the 
air  valve  in  the  same  manner  as  before  with  both  the 
full  and  the  small  load.  Repeat  until  very  slight  adjust- 
ments are  required  when  changing  from  one  load  to  the 
other. 

Put  on  the  small  load  and  adjust  the  ignition  for  the  least 
opening  of  the  throttle. 

If  the  throttle  continues  to  close  as  the  air  valve  is  adjusted 
up  to  its  limit  either  way  at  any  time  during  the  test,  then  the 
air  valve  should  be  set  nearly  to  its  other  limit  and  the  process 
of  adjustment  begun  again. 

When  the  limit  of  the  decrease  of  the  throttle  opening  is  not 
reached  by  adjusting  the  spring-closed  air  valve  from  one  ex- 
treme setting  to  the  other,  then  the  spring  is  either  too  weak  or 
too  strong,  provided  the  carbureter  is  otherwise  correctly  con- 
structed. 

If  the  initial  setting  of  the  spring  gave  the  lightest  pressure  of 
the  air  valve  on  its  seat,  and  the  adjustments  increased  the  seat- 
ing pressure  up  to  the  heaviest,  then  the  spring  is  too  weak. 
The  remedy  is  to  remove  the  spring  and  stretch  it,  if  it  is  a  com- 
pression spring,  so  as  to  close  the  valve  harder.  The  stretching 
must  give  the  spring  a  permanent  elongation  when  it  is  free. 
A  tension  spring  (seldom  used)  must  be  shortened  under  similar 
conditions. 


196  THE  GAS  ENGINE 

The  reverse  of  the  above  applies  to  the  spring  when  its  initial 
setting  gives  the  heaviest  pressure  of  the  valve  on  its  seat. 

The  fuel  valve  may  be  slightly  closed  from  the  adjustment 
determined  as  above  in  order  to  secure  the  best  economy  of 
fuel. 

The  ignition  should  finally  be  set  to  correspond  with  the  pre- 
vailing load,  using  at  least  two  of  the  settings  just  determined 
as  a  guide,  but  it  should  not  be  set  so  early  as  to  cause  thump- 
ing of  the  motor  on  full  load. 

129.  Adjustment  of  a  Variable-Speed  Motor  with  Hand  Con- 
trol by  Throttle.  —  (See  rough  adjustments. )  In  a  hand-con- 
trolled variable-speed  motor  the  throttle  and  the  ignition  are 
both  operated  by  hand  when  controlling  the  motor,  except  in 
infrequent  designs  where  the  time  of  ignition  is  not  changed. 

The  following  method  of  adjusting  the  carbureter  applies  to 
motors  in  which  both  the  throttle  and  the  ignition  are  manipu- 
lated for  controlling. 

The  adjustment  requires  the  load  to  be  rapidly  varied  at  will, 
as  by  an  absorption  dynamometer. 

After  each  adjustment  or  set  of  adjustments  is  made,  the 
throttle  may  be  quickly  operated  between  the  open  and  the 
nearly  closed  positions  (not  completely  closed).  If  this  causes 
either  back  firing  or  smoky  exhaust,  further  adjustment  of  the 
carbureter  should  be  made  before  testing  any  more.  If  there 
is  black  smoke,  the  air  valve  generally  should  be  opened  more; 
if  there  is  back  firing,  the  air  valve  should  generally  be  closed 
some.  Adjustments  the  reverse  of  these  are  sometimes  re- 
quired, however,  this  depending  on  the  form  of  the  carbureter. 
If  misfiring  occurs  with  neither  black  smoke  nor  back  firing  while 
the  throttle  is  quickly  operated,  the  fuel  valve  can  be  adjusted, 
but  whether  more  or  less  fuel  is  needed  cannot  be  determined 
before  making  an  adjustment. 

i.  Adjust  the  air  valve  to  about  mid-position;  set  the  ignition 
late  and  the  throttle  to  give  nearly  maximum  speed  with  no  load 
or  a  very  small  load.  Put  on  a  small  load  and  open  the  throttle 
till  the  speed  is  well  up  to  the  maximum.  Increase  the  load 
and  open  the  throttle  still  more  till  the  speed  is  nearly  up  to  the 


STARTING  AND  ADJUSTING  THE  MOTOR  197 

maximum  again.  Continue  the  increase  of  thjs  load  and  the 
opening  of  the  throttle  till  the  latter  is  full  open.  Then  advance 
the  timer  and  increase  the  load  till  the  setting  of  the  ignition  that 
pulls  the  greatest  load  at  somewhat  less  than  maximum  speed 
is  determined.  Now  adjust  the  fuel  valve  and  timer  to  increase 
the  speed  till  the  maximum  is  reached.  Retard  the  timer  slightly, 
put  on  more  load,  and  adjust  the  fuel  valve  and  timer  again  till 
the  maximum  speed  is  reached.  Continue  till  the  settings  that 
give  the  greatest  load  at  full  speed  are  found. 

2.  Retard  the  timer  and  increase  the  load  till  the  motor  is 
brought  down  to  a  slow  speed.     Adjust  the  air  valve  and  ignition, 
and  increase  the  load  till  the  greatest  load  that  the  motor  will 
pull  at  slow  speed  is  determined. 

3.  Set  the  air  valve  about  midway  between  its  last  two  positions 
and  repeat  the  operations  and  adjustments  of  (i). 

4.  Repeat  the  operations  of  (2). 

5.  Continue  the  adjustments  as  above  till  there  is  not  much 
change  of  setting  for  the  maximum  and  slow  speeds  with  heavy 
loads.     Make  the  last  adjustment  of  the  air  valve  as  in  (2). 

6.  Set  the  throttle  about  one-quarter  open  and  adjust  the  air 
valve  to  the  setting  that  gives  the  most  satisfactory  operation  at 
all  speeds  with  light  load.     The  ignition  must  also  be  adjusted 
during  this  test,  of  course.     Just  what  is  the  most  satisfactory 
operation  of  the  motor  depends  on  the  nature  of  the  service 
required. 

7.  Set  the  air  valve  about  two-thirds  of  the  way  back  toward 
the  last  setting.     Give  the  throttle  full  opening  and  adjust  the 
fuel  valve  to  give  the  best  results  at  maximum  speed.     If  these 
fall  much  below  what  was  obtained  in  (i),  the  test  should  be 
started  over  again  with  a  different  setting  of  the  air  valve  from 
that  in  (i). 

If  the  power  continues  to  increase  as  the  air  valve  is  adjusted 
up  to  its  limit  either  way  at  any  time  during  the  test,  then  the 
air  valve  should  be  set  to  its  other  limit  and  the  series  of  tests 
begun  again.  (See  latter  half  of  preceding  section.) 


198  THE   GAS  ENGINE 

130.  Adjustment  of  the  Carbureter  on  an  Automobile.  —  The 

following  is  such  an  adjustment  as  can  be  made  on  the  road 
without  any  apparatus  other  than  the  automobile  itself. 

1.  Set  the  air  valve  at  about  mid-position. 

2.  Open  the  throttle  half  way  or  less. 

3.  Set  the  timer  for  late  ignition. 

4.  Disengage  the  clutch. 

5.  Start  the  motor. 

6.  Advance  the  timer  part  way. 

7.  Open  and  close  the  throttle  quickly  several  times  to  deter- 
mine how  rapidly  the  motor  speeds  up,  and  whether  there  is 
either  black  smoke  in  the  exhaust  or  back  firing.     Set  the  timer 
in  different  positions  while  doing  this. 

8.  If  back  firing  occurred,  open  the  fuel  valve  more,  or  close 
the  air  valve  some; 

If  black  smoke  (not  blue)  was  discharged,  close  the  fuel  valve 
some,  or  open  the  air  valve  more; 

Test  after  each  adjustment  by  opening  and  closing  the  throttle 
at  different  settings  of  the  timer  until  the  motor  operates  satis- 
factorily. 

9.  Test  the  motor  by  climbing  a  hill  or  by  noting  the  rate  of 
speed  acceleration  on  a  level  road. 

10.  Adjust   the  fuel  valve   (without    changing  the  air-valve 
setting)  till  the  best  running  of  the  car  is  obtained. 

11.  Change  the  air-valve  setting  and  repeat  (10). 

12.  Change    the   air-valve    settings   again   and   repeat    (10). 
Continue  in  this  manner  till  the  settings  of  the  air  valve  and  the 
fuel  valve  that  give  the  most  satisfactory  operation  are  deter- 
mined. 

131.  Adjusting   the   Carbureter   and   Ignition   on   a  Launch 
Motor.  —  The  requirements  for  power  in  this  case  are  much  like 
those  for  an  automobile  motor,  but  simpler.     There  is  no  demand 
for  maximum  torque,  or  turning  effort,  at  slow  speed  of  the  motor 
in  a  launch. 

Apply  such  of  the  steps  for  the  automobile  as  are  necessary. 
The  object  is  to  secure  maximum  speed  of  rotation. 


STARTING  AND  ADJUSTING  THE  MOTOR  199 

Adjusting  the  Fuel  Mixture  in  Gas  and  Oil  Motors. 

132.  The  securing  of  a  suitable  proportion  of  gas  and  air  for 
a  combustible  mixture  is  a  much  simpler  operation  for  the  gas 
motor  than  when  the  air  is  carbureted  by  the  vaporization  of  a 
volatile  liquid. 

In  the  simpler  designs  only  the  gas  valve  is  set  by  trial  to  the 
position  that  gives  the  greatest  power,  speed,  etc.,  as  is  desired. 

The  more  complicated  designs  of  gas-and-air  mixers  have 
adjustments  for  both  the  gas  and  the  air  in  some  cases.  Since 
the  process  of  adjusting  is  so  simple,  it  seems  hardly  necessary 
to  give  the  steps  in  detail. 

It  is  generally  more  economical  of  fuel  to  close  the  gas  valve 
slightly  after  the  adjustment  for  maximum  power  has  been  found. 

In  some  designs  of  gas  motors,  the  securing  of  the  proper 
mixture  proportions  is  largely  a  matter  of  selecting  the  proper 
proportions  in  designing.  Designing  is  not  under  consideration 
in  this  part  of  the  discussion. 

The  above  statements  also  apply  in  a  general  way  to  oil  motors 
in  which  the  oil  is  injected  into  the  combustion  space.  The 
regulation  of  the  fuel  is  generally  by  varying  the  stroke  of  the 
piston  of  the  oil  pump,  by  opening  a  by-pass  valve,  etc. 


CHAPTER  IX. 
SETTING  OR  TIMING  THE  VALVES   AND   IGNITER. 

133.  Marks  for  Valve  Setting.  —  A  large  number  of  motors, 
especially  those  on  automobiles,  have  marks  on  the  flywheel  to 
indicate  its  positions  when  the  valves  should  begin  to  open  and 
complete   their   closing.      One  of    the   marks  on  the  flywheel 
registers  with  a  reference  mark,  that  is  stationary  with  regard  to 
the  frame  of  the  motor,  at  the  instant  that  the  corresponding 
valve  should  just  begin  to  open,  and  another  mark  on  the  flywheel 
registers  with  the  same  reference  point  at  the  time  the  valve 
should  just  come  in  contact  with  its  seat. 

Since  the  mark  on  the  flywheel  is  often  a  line  drawn  across  its 
face  in  a  direction  parallel  to  the  shaft,  or  radially  across  the  side 
of  the  rim,  and  since  the  stationary  part  is  often  a  pointed  piece 
of  metal,  they  will  be  referred  to  as  the  flywheel  mark  and  the 
reference  point,  or,  more  briefly,  as  the  mark  and  the  point,  for 
convenience. 

134.  Testing  the  Valve  Timing  when  the  Flywheel  is  Marked. 
—  The  simplest  case  is  a  single-cylinder,  single-acting  motor  with 
an  automatic  inlet  valve  and  one  exhaust  valve  (which  must  be 
mechanically  opened).      (There  are   sometimes   two   mechani- 
cally opened  exhaust  valves  when  an  auxiliary  exhaust  port  is 
used.) 

To  test  the  valve  setting:  Insert  a  piece  of  very  thin  tissue 
paper  (thick  paper  will  not  do)  between  the  end  of  the  valve  stem 
and  the  part  that  lifts  it.  Rotate  the  motor  by  hand  or  any  other 
suitable  means  till  the  piston  and  other  parts  are  in  the  position 
of  about  three-quarters  of  the  impulse  stroke.  Then  turn  the 
shaft  very  slowly  in  the  direction  that  it  runs  and  keep  the  paper 
moving  at  the  same  time  till  it  is  pinched  tight  by  the  movement 
of  the  valve-lifting  mechanism  toward  the  valve  stem.  Stop  in 

200 


SETTING  OR  TIMING  THE  VALVES  AND  IGNITER      2OI 

this  position.  If  the  valve  setting  is  correct,  tfre  mark  on  the 
flywheel  will  register  with  the  reference  point. 

If  the  mark  has  not  yet  reached  the  point  when  the  paper  is 
first  pinched,  then  the  valve  opens  too  early  according  to  the 
marking.  But  if  the  mark  has  passed  the  point,  then  the  valve 
does  not  open  soon  enough. 

For  the  closing  of  the  valve,  rotate  the  crank  shaft  quickly 
through  about  half  a  revolution  in  the  direction  that  the  motor 
runs  without  paying  any  attention  to  the  paper  under  the  valve 
stem.  Then  turn  the  crank  shaft  very  slowly  while  pulling  on 
the  paper  till  it  begins  to  loosen  on  account  of  the  seating  of  the 
valve  and  the  reduction  of  pressure  against  the  valve  stem.  If 
the  second  flywheel  mark  and  the  reference  point  register  at  the 
instant  the  paper  begins  to  loosen,  then  the  time  of  valve  closing 
is  correct  according  to  the  marking.  If  the  mark  has  not  yet 
reached  the  point,  the  valve  closes  too  early,  but  if  the  mark  has 
passed  the  point  the  valve  closes  too  late. 

When  the  inlet  valve  is  mechanically  operated,  its  setting 
can  be  tested  in  the  same  manner  as  that  for  the  exhaust  valve. 
The  exhaust  valve  should  always  be  closed  before  the  inlet 
valve  begins  to  open,  in  motors  of  the  usual  construction  with- 
out provision  for  scavenging.  This  can  be  determined  without 
any  markings  on  the  flywheel. 

In  a  two-cylinder  motor  with  either  opposed  or  twin  cylinders, 
whose  explosions  occur  every  revolution,  the  same  marking  of 
the  flywheel  serves  for  both  cylinders. 

In  a  four-cylinder  motor,  either  with  all  the  cylinders  on  one 
side  of  the  crank  shaft  or  with  two  on  each  side,  whose  explo- 
sions come  every  half  revolution,  there  must  be  two  sets  of  mark- 
ings. One  set  is  the  same  as  the  other,  but  half  way  round  the 
flywheel  from  it. 

In  a  six-cylinder  motor  with  the  cranks  in  pairs  at  120 
degrees  apart  and  the  cylinders  all  on  the  same  side  of  the 
crank  shaft,  there  are  three  sets  of  markings,  one  third  of  a 
revolution  apart. 

The  gears  that  connect  the  cam  shaft  to  the  crank  shaft  should 
be  marked  so  that  they  can  be  placed  together  again  with  the 


202  THE   GAS   ENGINE 

same  teeth  mating  as  before,  in  case  of  their  being  taken  apart. 
Some  manufacturers  mark  the  gears  for  this  purpose. 

135.  Locating  Dead  Centers  when  there  are  no  Marks  for 
Valve  Setting.  —  If  there  is  no  marking  for  the  valve  setting  or 
for  the  dead-center  positions  of  the  crank,  then  the  latter  should 
be  determined. 

To  determine  the  dead  centers,  some  means  of  locating  the 
position  of  the  piston  is  necessary.  When  there  is  a  'pet-cock 
with  a  straight  passage  in  the  cylinder  head,  and  the  length  of 
the  passage  is  parallel  to  the  bore  of  the  cylinder,  this  can  be 
done  by  inserting  a  straight  wire  through  the  pet -cock  till  the  end 
touches  the  piston.  The  wire  should  be  of  about  the  same  size 
as  the  hole.  If  the  head  of  the  piston  is  flat,  the  wire  will  always 
enter  the  same  distance  for  the  same  position  of  the  piston. 
But  if  the  piston  head  is  not  flat,  care  must  be  taken  to  insert 
the  wire  so  that  it  will  always  enter  the  same  distance  for  a  given 
position  of  the  piston.  Any  opening  through  the  cylinder  head, 
as  that  for  the  ignition  plug  of  the  pet-cock,  can  be  used  for 
inserting  the  wire  after  the  part  is  removed.  If  there  is  no  open- 
ing in  the  cylinder  head,  then  the  position  of  the  piston  can  be 
determined  from  the  crank  end  of  the  cylinder.  The  crank  case 
may  have  to  be  opened  for  this  purpose.  The  general  method  of 
procedure  is  the  same  in  all  cases  when  the  cylinder  is  not  offset 
(set  to  one  side  so  that  the  center  line  of  the  bore  does  not 
intersect  the  axis  of  the  crank  shaft). 

Offset  cylinders  are  unusual.  The  method  of  determining  the 
dead  centers  will  therefore  be  given  only  for  those  whose  crank 
shaft  crosses  in  front  of  the  center  of  the  cylinder  bore.  It  will 
be  assumed  that  there  is  a  suitable  pet-cock  for  inserting 
the  wire. 

Put  the  wire  into  the  cylinder  through  the  pet-cock  till  its  end 
rests  against  the  piston  and  rotate  the  crank  shaft  through  about 
one  revolution.  Note  roughly  the  positions  of  the  wire  while 
resting  against  the  piston  at  each  end  of  its  stroke.  Make  a 
notch  in  the  wire  at  a  position  that  will  coincide  with  the  end 
of  the  pet-cock  when  the  piston  is  about  one-third  of  the  way  out 
from  its  position  nearest  the  head  of  the  cylinder.  This  notch 


SETTING  OR  TIMING  THE  VALVES  AND   IGNITER      203 

can  be  located  by  judgment  without  measuring.  Place  the  wire 
against  the  piston  as  before  and  turn  the  crank  shaft  till  the 
notch  on  the  wire  registers  with  the  end  of  the  pet-cock.  Make 
a  temporary  mark  on  the  face  of  the  flywheel  to  coincide  with 
a  stationary  reference  point.  Rotate  the  crank  again  through 
part  of  a  revolution  till  the  notch  on  the  wire  again  registers 
with  the  end  of  the  pet-cock.  Mark  the  flywheel  again  as  be- 
fore to  coincide  with  the  reference  point.  Divide  the  shortest 
length  of  the  periphery  of  the  flywheel  between  the  two  marks 
just  made  on  it  into  halves  and  make  a  third  mark  midway 
between  the  other  two.  When  the  last  mark  registers  with  the 
stationary  reference  point,  the  crank  will  be  in  its  dead-center 
position  with  the  piston  at  the  head  end  of  its  stroke. 

The  dead-center  position  with  the  piston  at  the  crank  end  of 
its  stroke  can  be  determined  in  a  similar  manner  by  placing 
another  notch  on  the  wire  where  it  will  coincide  with  the  end  of 
the  pet-cock  when  the  piston  is  about  one-third  of  the  way  from 
the  crank  end  of  the  cylinder.  The  two  dead-center  marks  will 
be  1 80  degrees,  or  half  the  circumference  of  the  flywheel,  apart, 
if  correctly  located. 

When  there  is  no  flywheel,  or  it  is  difficult  of  access,  some 
other  rotary  part  can  be  used  in  the  same  manner.  In  small 
motors,  the  starting  crank  can  be  used  as  the  hand  (as  of  a  clock) 
and  a  board  or  piece  of  cardboard  provided  for  a  dial. 

136.  Time  at  which  a  Valve  should  Open  and  Close.  —  In  a 
four-cycle  motor,  the  exhaust  valve  should  open  long  enough 
before  the  piston  reaches  the  end  of  its  impulse  stroke  to  allow 
the  pressure  in  the  cylinder  to  drop  nearly  to  atmospheric  by 
the  time  the  piston  has  moved  an  appreciable  distance  on  the 
exhaust  stroke,  and  should  not  close  before  the  end  of  the  exhaust 
stroke.  The  smaller  the  port  and  the  less  the  lift  of  the  valve, 
the  earlier  must  it  open  and  the  later  it  must  close. 

A  mechanically  operated  inlet  valve  should  not  open  before 
the  exhaust  valve  has  closed,  and  should  remain  open  at  least 
until  the  suction  stroke  is  completed. 

The  time  at  which  a  valve  must  open  and  close  in  relation  to 
the  position  of  the  piston  in  its  movement  in  order  to  develop 


204  THE  GAS  ENGINE 

the    most    power  depends   principally   on  the  following    three 
items : 

Speed  of  rotation  of  the  motor; 

Area  of  the  ports  in  relation  to  the  volume  of  the  cylinder, 

or  of  the  piston  displacement  per  stroke; 
Lift  of  the  valve. 

Among  other  features  (which  should  all  be  minor  ones) 
affecting  the  valve  timing  are  the  back-pressure  resistance  to 
the  exhaust  and  the  suction  resistance  to  the  intake  due  to  causes 
outside  of  the  motor  proper. 

In  high-speed,  single-acting,  four-cycle  automobile  motors  the 
exhaust  valve  is  sometimes  set  to  open  as  much  as  40  degrees 
(one-ninth  of  a  revolution)  of  rotation  of  the  crank  before  the 
piston  has  reached  the  end  of  its  impulse  stroke,  and  does  not 
close  until  as  late  as  10  degrees  (one-thirty-sixth  of  a  revolution) 
after  the  completion  of  the  exhaust  stroke.  In  such  a  case  the 
inlet  valve  does  not  generally  open  earlier  than  15  degrees  (one- 
twenty-fourth  of  a  revolution)  of  rotation  on  the  suction  stroke. 
It  sometimes  closes  the  same  amount  later  on  the  compression 
stroke. 

The  proportion  of  the  stroke  of  the  piston  represented  by 
these  angles  of  rotation  is  not  as  great  as  it  might  at  first  seem, 
especially  at  the  crank  or  exhaust  end  of  the  stroke,  where  the 
angularity  of  the  connecting  rod  brings  the  piston  nearer  the 
end  of  its  stroke  than  it  is  from  the  completion  of  its  stroke  at 
the  head  end  when  the  crank  is  the  same  part  of  a  revolution 
from  the  head  dead  center. 

When  the  length  of  the  connecting  rod  is  twice  that  of  the 
stroke  of  the  piston  (connecting-rod  length  =  four  times  the 
crank  radius),  which  does  not  differ  much  from  automobile 
motor  practice,  and  the  crank  is  40  degrees  from  the  dead-center 
position  between  the  impulse  and  exhaust  strokes  (crank  dead 
center),  the  piston  has  only  .091  (less  than  one-tenth)  of  its 
stroke  remaining  to  complete  the  impulse '  stroke.  When  the 
exhaust  valve  closes  10  degrees  after  the  completion  of  the 
exhaust  stroke,  the  piston  has  moved  out  only  .0095  (less  than 


SETTING  OR  TIMING  THE  VALVES  AND  IGNITER      205 

one-hundredth)  of  the  suction  stroke  from  the  hea/1  end  When 
the  inlet  valve  opens  at  15  degrees  of  the  crank  past  dead 
center,  the  piston  has  moved  out  .021  (a  little  more  than  one- 
fiftieth)  of  its  stroke  from  the  head  end.  And  if  it  closes  at  the 
same  angle  of  the  crank  past  the  crank  dead  center,  then  the 
piston  has  moved  out  .013  (a  little  more  than  one-eightieth)  of 
its  stroke  from  the  crank  end. 

The  writer's  experience  in  increasing  the  power  development 
of  motors  by  changing  the  timing  of  the  valves  on  a  number  of 
automobile  motors  of  different  makes  in  which  the  exhaust  and 
inlet  valves,  as  originally  timed,  closed  at  or  near  the  dead-center 
positions  of  the  crank,  or  the  exhaust  valve  opened  only  slightly 
before  the  dead-center  position,  or  in  which  all  three  of  these 
conditions  existed,  has  been  thoroughly  convincing  in  favor  of 
early  openings  and  late  closings  to  conform  more  or  less  nearly 
with  those  just  mentioned,  according  to  speed,  area  of  ports, 
lift  of  valves,  etc.  In  some  cases  the  only  change  was  to  set  the 
cam  shaft  a  little  earlier  in  relation  to  the  crank  shaft,  while  in 
others  new  cams  were  made. 

In  moderate-  and  slow-speed  motors  on  which  an  indicator 
can  be  used  without  the  inertia  effects  of  its  moving  parts  causing 
serious  modification  of  the  true  indicator  card,  the  card  can  be 
used  to  determine  the  correctness  of  the  valve  action.  This  will 
be  discussed  later  (see  Indicator  diagrams).  In  very  high-speed 
motors  the  power  test  is  all  that  can  be  applied  for  this  purpose. 
The  power  test  is  the  crucial  one  in  all  cases. 

137.  Marking  the  Flywheel  for  Valve  Setting.  —  After  the 
times  of  opening  and  closing  of  the  valves  have  been  decided 
upon,  the  flywheel  can  be  marked  accordingly. 

If  the  exhaust  valve  is  to  begin  opening  at  one-ninth  of  a 
revolution  before  the  completion  of  the  exhaust  stroke,  measure 
from  the  crank  dead-center  mark  on  the  flywheel  (see  locating 
dead  centers)  one-ninth  of  the  circumference  around  in  the 
direction  of  its  rotation  and  mark  the  flywheel  accordingly 
(see  below  for  lettering).  If  the  exhaust  valve  is  to  close  one- 
thirty-sixth  of  a  revolution  after  the  completion  of  the  exhaust 
stroke,  measure  one-thirty-sixth  of  the  circumference  of  the  fly- 


206  THE  GAS  ENGINE 

wheel  from  the  head  dead-center  mark  in  the  direction  opposite 
that  of  the  rotation.  For  the  inlet  valve  to  open  one-twenty- 
fourth  of  a  revolution  after  dead  center,  measure  from  the  same 
(head)  dead -center  mark  one-twenty-fourth  of  the  circumference 
in  the  same  direction  (opposite  the  rotation).  And  for  the  inlet 
valve  to  close  15  degrees  after  the  dead  center,  measure  one- 
twenty-fourth  of  the  circumference  from  the  crank  dead-center 
mark  in  the  direction  opposite  the  rotation. 

The  marks  on  the  flywheel  should  be  lettered  to  avoid  con- 
fusion, especially  in  multi-cylinder  motors.  The  following 
lettering  is  suggested.  A  numeral  can  be  placed  after  the 
letters  of  each  marking  to  indicate  to  which  cylinder  or  com- 
bustion chamber  it  refers.  If  the  same  mark  is  for  more  than 
one  valve,  the  corresponding  numerals  can  be  placed  after  the 
letters. 

HC  =  head  center. 
CC  =  crank  center. 
EO  =  exhaust  opens. 
EC  =  exhaust  closes. 
IO  =  inlet  opens. 
1C  =  inlet  closes. 
EO  1-3  =  exhaust  opens  for  cylinders  i  and  3. 

138.  Effect  of  Worn  and  Loose  Parts  on  the  Valve  Action.  — 
A  cam  shaft  whose  driving  mechanism  has  become  worn  so 
that  the  shaft  lags  behind  its  correct  position,  retards  both  the 
opening  and  the  closing  of  a  valve.  A  cam  whose  fastening  is 
loose  so  that  the  cam  lags  produces  the  same  effect. 

A  loose  cam  that  lags  when  opening  a  valve  and  then  snaps 
forward  under  the  pressure  of  the  valve  spring,  retards  the  time 
of  opening  and  allows  the  valve  to  close  too  early,  thus  decreas- 
ing the  duration  of  the  open  period. 

Wear  of  any  part  of  the  valve-operating  mechanism  of  the  usual 
construction,  other  than  wear  that  allows  a  cam  to  lag  as  stated, 
causes  late  opening  and  early  closing,  shortening  the  duration  of 
the  opening. 


SETTING  OR  TIMING  THE  VALVES  AND  IGNITER       207 

The  regrinding  of  a  valve  down  on  its  seat  has  the  effect  of 
lengthening  the  valve  stem.  This  causes  early  opening  and  late 
closing,  which  is  compensative  with  the  wear  of  the  parts. 

The  methods  of  applying  the  remedies  for  the  above  troubles 
depend  on  the  construction  of  the  motor.  When  a  lifting  rod 
or  a  push  rod  is  used  for  raising  a  valve,  it  is  often  made  with 
some  provision  for  adjusting  its  length.  This  affords  a  means 
of  compensating,  more  or  less  completely,  wear  of  all  the  usual 
kinds  except  that  which  allows  a  cam  to  lag  or  turn  slightly  on 
its  shaft.  When  no  provision  for  adjustment  is  made,  the  push 
rod  or  the  valve  stem  can  be  cut  off  when  necessary,  or  if  it 
needs  lengthening,  a  thimble-shaped  cap  can  be  placed  over  its 
end,  or  a  pin  inserted  in  the  end  to  lengthen  it.  The  pin  may 
have  an  enlarged  end  to  resist  wear.  In  some  designs  the  push 
rod  is  a  short  round  bar  inserted  between  the  valve  stem  and 
the  lifting  mechanism.  A  new  push  rod  of  this  form  can  be 
substituted  readily  at  small  expense,  or  in  an  emergency  it  can 
be  elongated  by  hammering. 

A  worn  cam  can  be  built  up  by  brazing  or  riveting  a  piece  on 
it,  first  cutting  away  a  portion  if  better  results  can  be  thus  ob- 
tained. In  case  of  doubt  as  to  the  exact  form  of  the  cam,  it  can 
be  left  a  little  full  for  the  first  trial  of  the  valve  action  and  then 
cut  down  accordingly. 

139.  Adjusting  the  Ignition  Timer.  —  When  a  battery  and  an 
induction  coil  are  used,  the  following  method  can  be  applied: 
Open  the  pet -cocks  of  the  combustion  chambers,  or  remove  the 
spark  plugs  or  disconnect  the  wires  leading  to  them.  Set  the 
crank  shaft  on  dead  center  with  one  piston  at  the  end  of  its 
stroke  between  compression  and  impulse.  Set  the  hand  control 
a  little  in  advance  of  the  retard,  or  late  ignition,  position.  Turn 
the  rotor  of  the  timer  in  the  direction  that  it  is  to  rotate  until 
the  circuit  is  just  closed  and  a  spark  produced  for  the  cylinder 
whose  piston  is  set  as  given  above,  and  fasten  the  rotor  in  this 
position. 

If  the  speed  of  the  motor  is  too  high  when  running  with  a 
small  load,  the  throttle  well  closed  and  the  timer  retarded  as 
far  as  possible,  then  move  the  rotor  back  a  little  in  the  direction 


208  THE  GAS  ENGINE 

opposite  its  rotation,  or  adjust  the  connecting  mechanism  so 
that  the  stationary  part  of  the  timer  is  moved  further  in  the 
direction  of  rotation  of  the  rotor. 

For  an  oscillating  magneto  the  method  of  adjusting  is  the 
same  in  a  general  way.  The  part  that  engages  with  the  lever  or 
arm  of  the  armature  must  be  set  so  that  the  parts  will  disengage 
at  the  proper  instant. 

In  low-tension  ignition  with  cams  to  operate  the  contact 
points  of  other  mechanism,  the  method  of  setting  the  ignition 
cams  is  similar  to  that  for  timing  the  valves. 

A  high-tension  magneto  with  a  rotary  armature  should  have 
some  part  of  the  rotor  or  its  attachments  marked  to  indicate  the 
position  when  the  timer  closes  the  circuit.  In  the  absence  of 
such  marking,  the  current  from  a  battery  or  a  lighting  circuit 
can  be  used  to  determine  the  instant  that  the  timer  closes  the 
circuit.  After  this  is  done,  the  process  of  setting  is  of  the  nature 
of  those  just  described.  If  current  from  a  lighting  system  is 
used,  there  should  be  an  incandescent  lamp,  water  resistance, 
etc.,  in  series  with  the  generator  in  order  to  keep  down  the 
current. 

140.  Comparing  the  Time  of  Ignition  in  Different  Cylinders. 
-  It  is  important  that  there  shall  be  very  little  variation  in  the 
time  of  ignition,  relative  to  the  positions  of  the  respective  pistons, 
in  the  various  cylinders  of  a  multi-cylinder  motor.  The  follow- 
ing method  can  be  used  for  testing  the  time  at  which  the  primary 
circuit  is  closed  in  a  jump-spark  system. 

Set  the  crank  shaft  in  one  of  its  dead-center  positions.  (See 
marking  the  flywheel  for  valve  setting.)  If  there  are  no  dead- 
center  marks  on  the  flywheel  or  elsewhere,  any  mark  or  marks 
arranged  to  come  opposite  a  stationary  reference  mark  at  such 
parts  of  a  revolution  as  correspond  to  the  intervals,  as  they 
should  be,  between  ignitions,  will  answer  equally  well.  (See 
impulse  frequency  for  different  arrangements  of  cylinders.) 

Advance  the  timer  of  a  jump-spark  system  from  the  retard 
position  (late  ignition)  till  the  primary  circuit  is  just  closed  and 
leave  the  tinier  in  that  position.  Rotate  the  crank'  shaft  in  the 
direction  of  running  and  note  whether  the  timer  always  closes  all 


SETTING  OR  TIMING  THE  VALVES  AND   IGNITER      209 

the  circuits  at  the  instant  the  timing  marks  register  with  the 
reference  point.  Only  a  very  slight  variation  from  this  condition 
is  allowable. 

If  the  primary  current  is  supplied  by  a  rotary  generator  driven 
by  the  motor  during  regular  service,  a  battery  or  other  source  of 
electricity  must  be  substituted  while  making  the  test. 

In  the  case  of  an  oscillating  generator  (magneto)  for  either 
high-tension  or  low-tension  ignition,  it  is  generally  sufficient  to 
determine  whether  the  armature  is  released  and  snaps  back  at 
the  same  relative  position  of  the  piston  for  each  cylinder  if  the 
speed  of  rotation  of  the  motor  is  not  high.  The  method  is 
practically  the  same  as  that  just  given.  If  the  speed  of  the  motor 
is  very  high,  a  test  should  also  be  made  to  determine  whether  the 
primary  circuit  is  always  closed  at  the  same  position  of  the  arma- 
ture in  its  snapping-back  motion,  or  whether  the  different  pairs 
of  contact  points  of  a  low-tension  system  separate  at  the  same 
position  of  the  armature. 

When  a  rotary  generator  is  used  for  the  low-tension  (arc, 
make-and-break,  break-and-make)  system,  a  battery  current  of 
a  few  volts  can  be  passed  through  the  contact  points  and  the  time 
of  their  separation,  as  indicated  by  the  interruption  of  the  current, 
determined  by  rotating  the  crank  shaft  slowly  and  noting  the 
position  of  the  timing  marks  as  above.  The  generator  circuit 
should  be  broken  before  connecting  the  battery  to  the  ignition 
system.  One  terminal  of  the  testing  circuit  can  be  connected  to 
the  metal  of  the  motor,  and  the  other  terminal  to  the  insulated 
member  of  the  ignition  plug. 


CHAPTER  X. 

TROUBLES,  REMEDIES  AND  REPAIRS. 

141.  When  operated  and  cared  for  with  as  much  care,  skill, 
and  knowledge  as  are  usual  for  steam  engines  and  boilers,  the 
internal-combustion  motor  is  as  reliable  as  the  steam  power  plant. 
On  account  of  the  adoption  of  gas  and  oil  motors  to  any  con- 
siderable extent  being  comparatively  recent,  as  compared  with 
steam  engines,  they  are  not  nearly  so  well  understood  by  many 
of  those  who  operate  them. 

The  aim  of  this  chapter  is  to  set  forth  some  of  the  many  troubles 
met  by  the  inexperienced,  together  with  the  means  of  preventing 
most  of  them  and  of  remedying  the  others.  In  many  cases  a 
difficulty  that  seems  insurmountable  in  the  presence  of  ignorance 
is  really  insignificant  when  understood. 

The  following  detailed  list  of  causes  of  trouble  may  seem  long. 
An  equally  long  one  can  be  made  for  steam  engines  and  their 
accessories.  The  writer  has  experienced  more  trouble  with  steam 
engines  than  with  internal-combustion  motors,  in  proportion  to 
the  number  of  each  dealt  with. 

Conditions  that  Cause  Trouble  and  Loss  of  Power. 

142.  Very  few  of  these    troubles   ever  occur  in  connection 
with  intelligent  operation,  ordinary  care  and  good  construction. 

IN  THE  MOTOR. 
Leaks  between  the  combustion  chamber  and  jacket  space: 

Cracked  cylinder; 

Leaky  joint  between  cylinder  head  and  barrel; 

Loose  plug  in  the  cylinder  wall; 

Blowhole  in  the  cylinder  wall; 

Porous  casting. 

210 


TROUBLES,  REMEDIES  AND  REPAIRS  211 

Leaks  in  the  cylinder  wall  between  the  combustion  space  and 

the  atmosphere: 
Ignition  plug  not  in  tight; 

Loose  insulation  or  leaky  packing  in  the  ignition  plug; 
Pet-cock  partly  open  or  not  in  tight. 

Valve  leaks : 
Pitted  valve; 
Cracked  valve; 
Warped  valve; 

Flake  of  carbon  under  the  valve; 
Valve  stem  too  long  so  that  valve  cannot  rest  on  its  seat. 

Valve  binding  or  sticking: 

Carbon  deposit  on  the  valve  stem; 

Bent  valve  stem. 

Valve  spring  weak  or  broken. 

Piston  leaks: 

Scored  (grooved)  cut)  cylinder  wall  and  piston  rings; 

Piston  rings  broken,  worn,  or  improperly  fitted; 

Carbon  and  gummy  oil  under  the  piston  rings; 

Cracked  piston; 

Blowhole  in  piston; 

Carbon  deposit  on  the  cylinder  and  on  the  piston. 

IN  THE  COOLING  SYSTEM. 
Insufficient  water  or  oil  for  cooling. 
Inadequate  cooling  (radiating)  surface. 
Leaky  pump  packing  and  joints. 
Pump  not  operating  properly. 

Steam  from  hot  cylinders  forced  back  into  the  pump. 
Air  lock  in  the  circulating  system : 

Large  vertical  reverse  bends  in  the  connecting  pipes. 

Clogged  or  stopped  passages : 

Packing  or  gasket  squeezed  out  into  the  passage; 
Loose  lining  in  a  rubber  hose  acting  like  a  check  valve; 
Cotton  waste,  rags,  etc.,  in  the  passages; 
Short  kinks  in  a  hose  or  pipe  so  as  to  close  the  passage. 


212  THE   GAS  ENGINE 

IN  THE  CARBURETER. 

Passages  clogged  by  particles  of  foreign  matter  (dirt,  lint). 

Water  in  the  fuel  reservoir  of  the  carbureter. 

Flooding  on  account  of  the  float  binding  or  sticking  so  as  not 

to  rise  and  cut  off  the  inflow  of  fuel. 
Leaky  or  "water-logged"  float.     Causes  flooding. 
Valve  of  float  leaky  so  as  to  allow  flooding. 
Binding  or  sticking  of  the  air  valve. 
Broken  spring  on  the  air  valve. 
Frost  and  ice  in  the  mixture  passage. 
Air  lock  prevents  fuel  from  flowing  into  the  carbureter  after 

it  has  been  empty. 

* 

IN  THE  FUEL  AND  FUEL  SUPPLY. 

No  vent  in  the  fuel  tank. 

Air  lock  in  the  connections  between  the  fuel  tank  and  the 
carbureter. 

Pipes  stopped  by  gaskets,  short  bends  or  kinks,  lint,  etc. 

Water  in  the  fuel. 

Dirt  in  liquid  fuel. 

Dust  and  grit  in  the  gas,  as  in  imperfectly  cleaned  blast- 
furnace gas. 

Variation  in  the  quality  of  the  fuel  (liquid  or  gaseous). 

IN  THE  CONNECTIONS  BETWEEN  THE  CARBURETER  AND  MOTOR. 

Loose  joints  and  holes  through  which  air  can  leak  into  the 
mixture. 

IN  THE  IGNITION  SYSTEM. 
Spark  plug  defective  or  dirty: 

Carbon  and  oil  deposit  in  the  spark  gap  or  on  the  insulation; 
Spark  gap  too  wide  or  too  small; 
Carbon  on  the  contacts  of  the  low  tension  system; 
Contact-points  fuse  so  as  not  to  make  electric"  contact; 
Loose  contact  points; 


TROUBLES,   REMEDIES  AND   REPAIRS  213 

Water  on  the  points.     Generally  due  to  a  cracked  cylinder 

or  blowholes  in  the  cylinder  casting; 
Porcelain  insulation  cracked; 

Mica  insulation  loose,  open  between  the  disks  or  crumbled; 
Air  leaks  around  the  insulated  parts. 

Induction  coil: 

Contact  points  oxidized  or  fused  so  as  not  to  make  electric 

connection ; 

Dirt  or  other  foreign  matter  between  the  contact  points; 
Contact  points  fused  together; 
Bent  spring  (vibrator,  trembler,  interrupter); 
Loose  contact  points; 

Loose  connections  or  broken  wires  inside  the  coil  box; 
Defective  or  burned -out  insulation  in  the  coil  box; 
Difference  of  lag  in  producing  sparks  when  two  or  more 

coils  are  used  on  one  motor. 

Timer: 

Dirt  or  grit  between  contact  points; 

Springs  weak  or  broken; 

Loose  screws,  rivets,  etc.; 

Rotor  (rotating  part)  loose  on  its  shaft; 

Failure  to  make  contact  on  account  of  worn  parts; 

Circuit  closed  at  wrong  time  on  account  of  worn  or  loose 

parts. 
Shaft  not  in  continuous  electric  connection  with  the  metal 

of  the  motor  on  account  of  separation  by  oil  or  grease 

(unusual); 
Circuit  not   closed   at  the  same   relative  position  of  each 

piston  in  its  stroke. 

Battery: 

Connections  between  two  batteries  made  so  that  a  current 

flows  when  they  are  not  in  use; 
Exhausted  cells; 

No     insulation    (paper,    cardboard,    glass,    rubber,    etc.) 
between  the  metal  of  adjacent  cells; 


214  THE  GAS  ENGINE 

Binding  posts  of  different  cells  touch  each  other; 
Too  many  cells  for  the  induction  coil  (too  much  voltage); 
Cells  not   tightly   secured   to   prevent   shaking   about   and 
breaking  the  connections  between  them. 

Generator  (magneto  or  electromagnetic): 

Grease  and  dirt  on  the  commutator; 

Brushes  worn  or  bent; 

Commutator  worn  out  of  round,  loose,  or  with  poor  insula- 
tion; 

Brushes  binding  in  brush  holder  so  as  not  to  press  on  the 
commutator; 

Broken  wires  at  the  connections  or  inside  the  insulation; 

Defective  or  burned-out  insulation; 

Loose  parts; 

Magnetism  lost  (infrequent). 

Connections  (electric): 

Loose  binding  screws  and  joints; 

Poor  quality  of  insulation,  especially  on  the  high-tension 
circuit ; 

Broken  wires  at  the  binding  posts; 

Broken  wires  inside  the  insulation  (sometimes  very  diffi- 
cult to  find); 

Insulation  chafed  or  worn  off  so  as  to  allow  electric  contact 
with  metallic  parts.  This  may  be  only  intermittent  on 
account  of  a  swinging  or  vibrating  wire,  or  the  movement 
of  a  part  such  as  a  brake  rod,  clutch  lever,  etc. 

Symptoms  and  Diagnoses. 

143.  Back-firing  into  the  intake  pipe  and  carbureter  is  generally 
due  to  some  of  the  following  causes: 

Lean  mixture.  A  lean  mixture  may  be  due  to  leaks  at  the 
joints  of  the  intake  pipe  between  the  carbureter  and  motor,  or 
to  improper  adjustment  of  the  carbureter.  Water  in  gasoline 
will  cause  a  lean  mixture  temporarily; 


TROUBLES,   REMEDIES  AND  REPAIRS  215 

Carbon  deposit  on  the  piston  head  and  the  walls  of  the  com- 
bustion chamber; 

Overheating  of  the  cylinder,  piston,  ignition  points  or  exhaust 
valve,  or  of  a  projecting  piece  of  metal  in  the  cylinder; 

Excessive  rarefication  of  the  charge  by  throttling  or  cutting 
off  the  charge  in  the  very  early  part  of  the  intake  stroke,  and  the 
consequent  slow  burning; 

Binding  or  sticking  of  the  inlet-valve  stem; 

Weak  spring  on  the  inlet  valve,  especially  if  it  is  an  automatic 
valve; 

A  particle  of  carbon  scale  or  other  foreign  matter  under  the 
inlet  valve; 

It  is  impossible  to  prevent  back  firing  when  the  amount  of 
mixture  admitted  for  a  charge  is  about  as  small  as  will  ignite. 
The  remedy  is  either  to  cut  off  the  charge  completely  or 
to  admit  more.  Misfiring  is  apt  to  accompany  back  firing 
under  this  condition,  and,  less  frequently,  exhaust  explosions 
also  occur. 

If  preignition  occurs  in  connection  with  back  firing,  the  cause 
is  either  an  overheated  cylinder  or  other  part  in  the  combustion 
space,  or  incandescent  carbon  in  the  cylinder. 

If  the  gas  valve  or  carbureter  has  not  been  adjusted  and 
operating  satisfactorily,  and  back  firing  occurs  when  the  charges 
are  not  cut  down  excessively  in  amount,  the  carbureter  or  gas 
valve  may  need  adjustment. 

If  the  carbureter  has  been  operating  satisfactorily,  or  the  gas 
valve  (of  a  gas  motor)  has  been  adjusted,  then : 

Note  whether  the  cooling  water  or  cooling  oil  is  excessively  hot 
or  not  circulating  properly,  and 

Cut  off  the  ignition  completely  from  all  the  cylinders  to  see 
whether  the  explosions  continue  after  the  ignition  is  cut  off. 

If  the  explosions  continue  after  the  ignition  has  been  cut  off 
from  all  the  cylinders,  then  there  is  either  incandescent  carbon 
deposit  in  one  or  more  of  the  cylinders,  a  hot  point  or  projecting 
piece  of  metal,  or  there  is  overheating.  In  case  of  continued 


2l6  THE   GAS  ENGINE 

explosions,   and  if    they  do  not  continue  in   all  the  cylinders, 
then: 

Put  on  the  ignition  again  and  then  cut  it  off  from  one  cylinder 
at  a  time,  or  in  pairs,  to  determine  where  the  ignitions  occur 
without  the  aid  of  the  ignition  apparatus.  (See  cutting  out  the 
ignition.) 

If  the  explosions  do  not  continue  after  the  ignition  is  completely 
cut  off,  then: 

Note  the  setting  of  the  adjusting  (needle)  valve  of  the  carbu- 
reter, and  then  close  and  open  it  again  quickly  so  as  not  to  stop 
the  motor.  This  will  generally  remove  dirt  or  other  foreign 
matter  from  the  passage  at  the  needle  valve. 

Drain  the  carbureter  to  remove  water; 

Strike  the  carbureter  a  sharp,  light  blow  to  shake  the  float  loose 
in  case  it  is  sticking  in  such  a  position  as  to  keep  the  inlet  valve 
of  the  carbureter  partly  closed; 

Open  the  gas  valve  (of  a  motor  using  permanent  gas)  to  com- 
pensate for  the  fuel  becoming  more  lean; 

Stop  the  motor  and  examine  for  a  binding  or  sticking  valve 
stem  or  a  weak  spring  on  the  inlet  valve. 

Test  the  compression.     If  it  is  very  poor,  then: 

Turn  the  mechanical  inlet  valve  around  on  its  seat  while 
applying  enough  lifting  force  to  it  to  allow  it  to  press  lightly  on 
its  seat.  The  lifting  force  can  be  applied  by  the  valve-lifting 
cam  by  bringing  the  crank  shaft  to  a  position  where  the  valve 
just  begins  to  leave  or  to  settle  on  its  seat; 

Look  for  a  cracked  or  broken  inlet  valve. 

144.  Misfiring  not  accompanied  by  other  serious  troubles, 
but  sometimes  by  exhaust  explosions,  is  generally  due  to  one  or 
more  of  the  following  causes : 

Ignition  adjustment  or  trouble; 

Carbureter  adjustment  or  trouble  giving  too  rich  a  mixture 
and  causing  carbon  deposit  in  the  cylinder; 

Lubrication  excessive  or  oil  poor  in  quality  for  the  purpose; 

Valve  troubles  (infrequently). 

If  black  smoke  is  discharged  from  the  exhaust,  adjust  the 
carbureter  or  the  gas  valve  to  cut  down  the  fuel. 


TROUBLES,   REMEDIES  AND   REPAIRS  217 

If  blue  smoke  is  discharged,  either  cut  down*  the  amount  of 
lubricating-  oil  fed  to  the  cylinder  or  get  suitable  lubricating  oil 
for  it. 

Test  the  ignition  system  (see  ignition  system  tests.) 

Look  for  a  weak  exhaust-valve  spring  and  for  binding  or 
sticky  exhaust-valve  stems. 

Test  the  compression.     If  it  is  poor,  then: 

Twist  the  exhaust  valve  around  while  it  presses  lightly  on 
its  seat  to  remove  flake  carbon  or  other  foreign  matter  from 
under  it; 

Look  for  a  cracked  or  broken  exhaust  valve; 

Test  for  a  cracked  cylinder  or  a  leaky  plug  in  the  cylinder  wall 
between  the  combustion  chamber  and  water  jacket.  (See  test 
for  cracked  cylinder  and  loose  plug.) 

145.  Continuous    Pounding,   Thumping,   or    Hammering    on 
Heavy  Load.  —  When  not  accompanied  by  other  evidences  of 
trouble,  this  is  generally  due  to  one  of  the  following  faults : 

Loose  fit  between  the  connecting  rod  and  the  crank  pin  or 

the  wrist  pin  (piston  pin); 
Loose  bearings  on  the  crank  shaft; 
Fly  wheel  loose  on  its  shaft  (loose  key). 

The  piston,  if  rather  loose  in  the  cylinder,  may  also  thump  at 
each  explosion.  This  is  not  generally  serious,  although  the  noise 
may  be  disturbing. 

The  first  three  of  these  troubles  should  be  remedied  as  soon  as 
possible,  for  they  are  apt  to  be  the  sources  of  injury  to  the  parts 
on  account  of  the  heavy  pressures  produced  when  they  strike 
together  at  the  time  the  sound  is  produced.  The  bearings  are 
generally  constructed  so  that  the  lost  motion  can  readily  be 
taken  up. 

146.  Preignition  and  Sharp  Snaps  or  Heavy  Pounding  in  the 
Motor.  —  If  the  igniter  is  not  set  to   give  too  early  ignition,  pre- 
ignition  is  generally  due  to  either  an  overheated  cylinder,  carbon 
deposit,  or  hot  ignition  points  or  projections  in  the  combustion 


21 8  THE  GAS  ENGINE 

chamber.  It  also  occurs  when  the  motor  compresses  the  charge 
more  than  is  allowable  for  the  kind  of  fuel  used. 

If  the  cylinder  is  overheated,  it  may  be  on  account  of  too  late 
ignition,  too  rich  a  mixture,  or  insufficient  lubrication.  The 
exhaust  pipe  will  generally  be  very  hot  (sometimes  red  hot)  if  the 
ignition  is  too  late  or  the  mixture  too  rich. 

Carbon  deposit  in  the  cylinder  will  cause  preignition  even  if  the 
cylinder  is  not  overheated  or  the  cooling  water  or  oil  not  hotter 
than  it  should  be. 

In  any  case  of  preignition  by  means  other  than  the  early  setting 
of  the  ignition  apparatus,  the  motor  may  continue  running  after 
the  ignition  is  cut  off,  and  may  kick  if  cranked  soon  after 
stopping.  (See  carbon  deposit  and  cooling-water  troubles. ) 

147.  Power  Decreases  Rapidly  at  a  Uniform  Rate  and  the 
Motor  Stops.  —  There  may  also  be  back  firing  and  misfiring 
just  before  the  motor  stops.  This  behavior  may  be  due  to  some 
of  the  following  troubles: 

No  fuel; 

Water  in  the  carbureter.     (Drain  it  out); 

Valve  suddenly  jarred  shut  in  the  fuel  pipe  or  the  carbureter; 

Broken  connection  in  the  fuel-supply  pipe. 

In  an  automobile  this  sudden  loss  of  power  will  occur  when  the 
fuel  tank  is  rather  empty  and  the  car  is  run  along  the  inclined 
side  of  the  road  so  that  the  end  of  the  tank  from  which  the  fuel  is 
drawn  is  on  the  high  side  of  the  car. 

It  also  occurs  when  the  fuel  (liquid)  is  low  and  the  car  turns  a 
curve  at  high  speed  so  as  to  throw  the  gasoline  away  from  the  out- 
let of  the  tank.  The  power  may  drop  off  and  then  come  on  again 
quickly  when  this  occurs.  The  action  is  especially  noticeable 
when  climbing  a  grade. 

The  remedies  to  the  above  troubles  are  obvious. 

To  drain  the  water  out  of  a  carbureter,  open  the  valve  at  the 
bottom  of  the  gasoline  reservoir  of  the  carbureter,  or  remove 
the  bottom  plug.  If  there  is  no  means  of  opening  the  bottom  of 
the  carbureter  for  drainage,  then  remove  the  top  and  siphon  the 
water  out  with  a  bent  tube  or  a  piece  of  small  rubber  hose.  Or 


TROUBLES,  REMEDIES  AND  REPAIRS  219 

it  can  generally  be  drawn  out  by  closing  the  air. inlet  with  one's 
hand  while  rotating  the  motor.  The  carbureter  can  be  removed 
and  emptied  without  much  trouble  in  some  cases. 

148.  Power    Decreases    Slowly   at  a   Uniform   Rate  and  the 
Motor  Finally  Stops.  —  This    may  be    accompanied    by  back 
firing  and  misfires  after  the  impulses  have  become  quite  weak. 

These  are  the  characteristic  symptoms  of  no  vent  in  the  fuel 
tank  of  a  vapor  motor  with  gravity  feed,  or  of  the  fuel  gas 
growing  poor  when  taken  from  a  gas  producer  about  as  fast  as  it 
is  made. 

The  gradual  jarring  shut  of  a  valve  in  the  fuel-supply  passages 
has  the  same  effect. 

The  opening  up  of  a  joint  or  a  valve  in  a  gas-supply  pipe  or 
in  the  mixture  passage,  so  that  air  is  admitted,  is  another  cause. 

149.  The    Motor    Behaves    Erratically  and  the  Timer  Con- 
trol Must  be  Set  Differently  from  Usual  Position  to  get  the  Best 
Results.  —  When  the  timer  rotor  (rotating  part)  is  very  loose 
on  its  shaft  these  results  often  occur.     They  are  apt  to  be  accom- 
panied by  preignition,  back  firing,  and  misfiring.     If  the  tinier 
rotor  takes  a  permanent  position  for  a  while  and  the  control 
agrees  with  it  the  motor  will  pull  well.    But  when  the  rotor  keeps 
moving  on  its  shaft  the  power  may  be  good  for  a  while,  and 
then  erratic  action  will  begin. 

150.  The  Motor  does  not  Develop  Full  Power  at  any  Time.  — 
When  not  accompanied  by  other  symptoms,  such  as  back  firing, 
misfiring,  overheating,  etc.,  this  is  generally  due  to  one  of  the 
following  causes: 

Insufficient  lubrication,  especially  of  the  cylinder; 
Piston  leaks; 
Valve  leaks; 

Particle  of  carbon  under  a  valve; 

Leaks  from  the  cylinder  into  the  atmosphere  through  or 
around  the  spark  plug,  pet -cock,  etc. 

The  motor  can  be  tested  for  some  of  the  leaks  while  running 
(see  running  test),  or  some  one  of  the  compression  tests  can  be 
applied  (see  compression  tests). 


220  THE  GAS  ENGINE 

In  the  case  of  a  leaky  valve  it  should  be  turned  around  while 
pressing  lightly  on  its  seat  in  order  to  remove  a  particle  of  carbon 
that  may  have  lodged  under  it. 

151.  The  Motor  Runs  Well  for  a  While,  then  Loses  Power 
and  the  Cooling  Water  Heats  Unduly.  —  These  are  the  symptoms 
of  an  opening  between  the  combustion  chamber  and  the  water 
jacket.  The  opening  may  be  on  account  of  a  loose  plug  in  the 
cylinder  wall  or  of  a  cracked  cylinder.  In  such  cases  the 
opening  closes  up  sometimes  when  the  motor  is  cool,  but  opens 
out  when  it  becomes  hot. 

The  opening  allows  the  hot  gases  of  combustion  to  pass  out 
into  the  cooling  water  and  heat  it,  and  also,  during  the  suction 
stroke,  some  of  the  water  or  steam  to  be  drawn  into  the  com- 
bustion chamber  from  the  water  jacket.  The  water  thus  drawn 
into  the  cylinder  is  almost  certain  to  cause  misfiring. 

After  the  motor  has  been  stopped  for  a  while  and  allowed  to 
cool  down,  it  will  sometimes  run  well  again  for  a  short  time  and 
then  behave  as  before. 

If  the  crack  or  opening  is  rather  large,  there  will  be  consider- 
able loss  of  compression  and  power  even  when  the  motor  is  cool. 

Any  of  the  hand  or  the  stationary  tests  for  compression  and 
leaks  can  be  applied,  but  in  case  they  do  not  show  leaks  between 
the  combustion  chamber  and  the  water  jacket,  then 

Apply  the  running  test  for  a  cracked  cylinder  and  loose  plug. 


CHAPTER  XI. 
TESTS   OF  IGNITION   SYSTEMS. 

152.  Test  of  High -Tension  (Jump-Spark)  Ignition  System 
with  Individual  Induction  Coils  and  Duplicate  Batteries.  —  [The 
test  when  the  primary  current  is  furnished  by  an  electric  generator 
(magneto)  is  practically  the  same  as  the  one  given  below,  but  the 
motor  must  be  kept  running  if  the  generator  is  of  the  rotary 
type.] 

It  is  assumed  that  one  of  the  batteries  is  held  as  a  reserve  and 
the  other  used  till  exhausted,  then  a  new  battery  put  in  and 
the  old  reserve  one  used  for  the  regular  service. 

Switch  on  the  reserve  battery  while  the  motor  is  running.  An 
exhausted  dry-cell  battery  often  works  well  for  a  short  time  after 
a  considerable  period  of  rest  and  then  fails  gradually. 

Press  down  the  tremblers  (vibrators,  interrupters)  one  at  a 
time,  or  in  pairs,  to  find  the  cylinder  in  which  the  misfiring  occurs. 
This  can  be  done  with  the  fingers. 

Note  whether  all  the  tremblers  vibrate  strongly.  If  this  cannot 
be  done  while  the  motor  is  running,  stop  it  and  either  rotate  it 
slowly  by  hand  or  close  the  battery  circuit  for  each  coil  in  turn  by 
placing  a  piece  of  metal  (wire,  screw-driver,  etc. )  so  as  to  connect 
the  timer  terminal  of  each  coil,  one  at  a  time,  to  the  metal  of  the 
motor  or  to  the  battery  terminal  of  the  timer. 

If  all  the  tremblers  have  weak  action,  then  look  for  loose 
connections  at  the  battery  and  between  the  timer  and  the  induc- 
tion coil.  Examine  the  battery  (low-tension,  primary)  circuit 
for  bare  places  and  wires  broken  inside  of  the  insulation.  See 
that  there  is  good  metallic  (electric)  connection  between  the  rotor 
of  the  timer  and  the  metal  of  the  motor,  or,  in  the  case  of  a  rotor 
that  is  insulated  from  its  shaft,  that  the  contact  is  good  between 
the  metal  of  the  rotor  and  the  part  to  which  the  wire  from  the 
battery  is  electrically  connected. 

221 


222  THE   GAS  ENGINE 

If  only  one  trembler  has  weak  action  (or,  more  strictly,  if  not 
all),  then  look  for  bare  and  broken  wires  and  loose  connections 
between  it  and  the  timer.  Clean  the  contact  points  of  the 
trembler  and  notice  whether  they  are  loose.  (See  induction-coil 
troubles.)  Close  the  circuit  at  the  timer  as  before  and  look  for 
troubles  in  the  circuit  for  the  coil  under  inspection.  (See  induc- 
tion-coil troubles.) 

Test  each  spark  plug  and  its  wire  in  turn  as  follows: 
Disconnect  the  high-tension  (secondary)  wire  from  the  spark 
plug,  hold  the  end  of  the  wire  about  one-quarter  of  an  inch  from 
the  metal  of  the  motor  or  of  the  spark  plug,  and  close  the  primary 
(battery)  circuit  for  that  plug.  A  spark  should  jump  the 
quarter-inch  air  gap  between  the  end  of  the  wire  and  the  motor 
or  spark  plug.  If  no  spark  jumps,  look  for  poor  insulation  on 
the  secondary  (high-tension)  wire  under  test; 

Remove  the  spark  plug  from  the  motor,  connect  the  high- 
tension  wire  to  it  again,  place  the  outer  metal  of  the  plug  against 
the  metal  of  the  motor,  and  close  the  primary  circuit  for  the  plug 
under  test.  If  both  sides  of  the  spark  plug  are  insulated  and  a 
wire  leads  to  each  side,  it  is  not  necessary  to  make  contact  with 
the  metal  of  the  motor  for  this  part  of  the  test.  There  should  be 
a  strong  spark  across  the  air  gap  of  the  plug.  The  spark  may  not 
jump  the  gap  when  the  plug  is  in  the  motor,  however,  even  though 
it  is  strong  outside,  for  the  reason  that  the  resistance  to  its 
jumping  is  much  higher  in  the  compressed  charge  in  the  motor 
than  in  the  open  air; 

Separate  the  spark  points,  if  possible,  so  as  to  have  a  spark  gap 
of  one-eighth  inch  or  slightly  more,  and  test  again  as  before. 
There  should  be  a  strong  spark.  Put  the  points  back  so  as  to 
have  a  spark  gap  of  about  one-thirty-second  (Jg-)  of  an  inch. 

If  the  spark  is  weak,  clean  the  plug  (see  cleaning  spark  plug) 
and  test  it  again  as  above.     If  the  result  is  not  satisfactory,  then : 
Put  in  a  new  plug,  or  new  insulation  in  the  old  one; 
Test  the  timer  for  uniformity  of  the  time  of  ignition.     (See 
comparing  the  time  of  ignition  in  different  cylinders. ) 

153-  Test  of  High-Tension  Distributer  Ignition  System  with 
Duplicate  Batteries.  —  (When  the  primary  current  is  furnished 


TESTS  OF  IGNITION  SYSTEMS  223 

by  a  generator,  the  test  is  the  same  except  that  the  motor  must  be 
kept  running  if  the  generator  is  of  the  rotary  type.) 

Switch  on  the  reserve  battery. 

Cut  off  the  ignition  from  the  cylinders,  one  at  a  time  or  in  pairs, 
while  the  motor  is  running,  by  short-circuiting  the  spark  plug  to 
determine  which  cylinder  is  misfiring.  The  short-circuiting  of 
the  spark  plug  can  be  done  with  a  wooden-handled  screw-driver 
placed  against  both  the  insulated  central  part  of  the  plug  and 
the  metal  of  the  motor,  or  across  the  insulated  parts  of  the  plug 
if  both  terminals  are  insulated.  Care  should  be  taken  to  hold 
the  tool  by  the  insulated  part  to  avoid  a  shock,  which,  while  not 
at  all  dangerous,  is  startling. 

If  there  is  misfiring  in  all  of  the  cylinders,  then : 

Look  for  loose  connections  in  the  battery  and  the  battery 

circuit ; 
Rotate  the  timer  and  distributer  arm  and  notice  whether 

the  arm  comes  near  or  opposite  the  high-tension  terminals 

at  the  instant  the  timer  closes  the  primary  circuit; 
Clean  the  vibrator  (trembler,  interrupter)  contacts  and  note 

whether  the  spring  is  bent; 
Test  each  spark  plug  and  its  connections  as  in  the  latter 

part  of  the  preceding  section. 

(See  also  "comparing  the  time  of  ignition  in  different  cylin- 
ders.") 

If  the  misfiring  does  not  occur  in  all  the  cylinders,  then : 

Examine  the  timer  contacts  for  the  cylinder  that  misfires; 
Apply  the  spark-plug  test  as  in  the  preceding  section. 

154.  Test  of  High-Tension  Magneto  Ignition  System.  —  Short- 
circuit  the  spark  plugs,  one  at  a  time  or  in  pairs,  as  in  the  pre- 
ceding section,  to  locate  the  misfiring. 

If  the  misfiring  is  general,  examine  the  magneto,  especially 
the  moving  contacts,  screw  fastenings,  and  the  connections.  (See 
magneto  test.) 


224  THE   GAS  ENGINE 

If  the  misfiring  is  confined  to  only  a  portion  of  the  cylinders, 
apply  the  spark-plug  test.  (See  individual  induction-coil  system. ) 

(Also  see  "  comparing  the  time  of  ignition  in  different  cylin- 
ders.") 

155.  Test  of  Low-Tension  Arc-Ignition  System.  —  This  test 
applies  more  especially  when  the  electric  generator  is  of  the 
rotary  type,  but  will  also  answer  for  the  oscillating  magneto 
generator. 

Cut  out  the  ignition  from  the  cylinders  successively  to  find 
which  is  misfiring.  This  can  be  done  by  opening  the  switches 
near  the  ignition  plugs,  or  by  disconnecting  the  wires  at  the 
plugs. 

If  the  misfiring  is  general,  then : 

Examine  the  generator  for  worn  or  loose  brushes,  com- 
mutator worn  out  of  round,  dirt  on  the  commutator, 
loose  connections,  etc.  (See  electric-generator  test); 

Clean  the  spark  plugs;  adjust  the  contacts  to  bring  fresh 
parts  together; 

Examine  the  spark  plugs  for  weak  springs  and  worn  parts. 

(Also  see  "comparing  the  time  of  ignition  in  different  cylin- 
ders.") 

If  the  misfiring  is  in  only  one  cylinder,  then  make  the  tests 
just  given,  but  reserve  the  examination  of  the  generator  till  the 
last. 

156.  Test  of  Magneto   Direct-Current  Electric  Generator.  - 
The  following  tests  can  be  applied  without  the  aid  of  much  appa- 
ratus in  case  the  generator  fails  to  operate  satisfactorily.     They 
apply  especially  to  a  magneto  which  has  a  commutator  with 
several  segments. 

See  that  the  brushes  press  against  the  commutator  so  as  to 
make  good  contact.  They  may  be  worn  out  or  bind  in  the  brush 
holder. 

Note  whether  the  commutator  is  round  and  runs  true. 

See  that  the  brushes  have  good  contact  with  their  holders. 

Examine  the  commutator  for  a  segment  with  a  blackened  or 
fused  edge.  This  may  be  caused  by  a  broken  or  loose  connec- 


TESTS  OF  IGNITION  SYSTEMS  225 

tion  between  the  segment  and  the  armature  winding,  or  by  a 
partly  burned  out  armature  coil.  The  edge  of  the  segment 
which  passes  under  the  brush  immediately  before  one  that  is 
dead  (connection  broken)  is  the  one  that  is  affected. 

Look  for  loose  and  broken  connections  in  both  the  generator 
and  the  outside  circuit. 

A  completely  burned  out  coil  can  generally  be  readily  seen  by 
an  examination  of  the  outside  of  the  armature. 

See  that  the  commutator  is  clean  and  free  from  grease  and 
dirt.  It  can  be  cleaned  by  holding  a  piece  of  fine  sandpaper 
(not  emery  paper  or  emery  cloth)  against  it  while  running.  It 
is  advisable  to  lift  the  brushes  while  cleaning  the  commutator 
in  this  manner.  Do  not  use  gasoline  to  cut  the  gum.  It  will 
be  ignited  by  the  spark  at  the  brushes. 

Test  the  strength  of  the  magnet  by  placing  a  piece  of  soft 
steel  or  iron  (as  a  steel  nail,  door  key,  screw-driver)  against  one 
of  the  poles  (ends)  of  the  magnet.  The  magnet  should  be 
strong  enough  to  hold  the  nail  tight,  even  to  hold  it  out  horizon- 
tally from  a  flat  surface,  especially  if  the  armature  of  the  gener- 
ator has  been  removed.  No  other  metal  or  non-ferrous  alloy 
will  do  for  this  test. 

A  weak  magnet  can  be  permanently  magnetized,  if  it  is  steel 
that  is  hardened  very  hard,  by  the  application  of  a  powerful 
magnet.  An  electromagnet  is  best  for  this  purpose.  To  remag- 
netize,  place  one  pole  of  the  electromagnet  (say  the  north  pole) 
near  the  middle  of  the  permanent  magnet  and  draw  the  electro- 
magnet along  the  metal  in  the  direction  toward  the  end  of  the 
hard  steel,  keeping  the  two  magnets  in  contact  during  the  mo- 
tion. Then  place  the  other  (south)  pole  of  the  electromagnet 
near  the  middle  of  the  permanent  magnet  and  draw  the  electro- 
magnet along  to  the  other  end  of  the  hard  steel.  By  repeating 
these  operations  several  times  the  hard  steel  will  be  fully  mag- 
netized and  will  remain  a  strong  permanent  magnet  if  the  steel 
is  hard  enough,  unless  some  demagnetizing  influence  other  than 
that  of  the  armature  currents  in  regular  service  acts  on  it.  Soft 
steel  will  not  retain  sufficient  magnetism  for  a  magneto  generator. 

The  following  test  can  be  made  with  a  portable  magneto  such 


226  THE  GAS  ENGINE 

as  is  used  with  telephones  in  which  the  magneto  crank  is  turned 
to  ring  the  bell  when  calling  central : 

Disconnect  all  wires,  etc.,  leading  out  from  the  magneto  to 
the  exterior  circuit. 

Lift  the  brushes  from  the  commutator.  Connect  the  terminals 
of  the  portable  magneto  to  the  brushes,  one  terminal  to  each 
brush  (of  the  two).  The  bell  of  the  testing  magneto  should  not 
ring  when  the  crank  of  the  testing  magneto  is  turned  rapidly  (or 
otherwise).  If  the  bell  rings,  the  insulation  of  the  brushes  is 
poor.  Test  the  insulation  between  the  armature  shaft  and  the 
brushes  in  the  same  manner.  If  the  bell  rings  in  either  case, 
remove  the  brushes  or  brush  holders  and  clean  the  insulation 
carefully. 

Connect  one  terminal  of  the  testing  magneto  to  the  armature 
shaft  of  the  generator  and  the  other  terminal  to  several  of  the 
commutator  segments  in  succession  while  turning  the  crank  of  the 
testing  magneto.  Turn  the  testing  magneto  rapidly.  If  the  bell 
rings  there  is  poor  insulation  between  the  armature  winding  and 
the  armature  core.  The  remedy  for  this  is  to  partly  or  wholly 
rewind  the  armature.  Some  armatures  are  made  so  that  a  section 
or  coil  of  the  winding  can  be  removed  and  another  section  put  in 
its  place  without  disturbing  the  other  sections. 

A  broken  or  loose  connection  may  make  intermittent  contact 
and  cause  erratic  behavior  of  the  generator. 

Put  one  of  the  brushes  down  against  the  commutator  so  that 
it  has  good  contact  (the  brush  can  be  held  as  usual  in  its  holder), 
connect  one  terminal  of  the  testing  magneto  to  the  brush,  and 
place  the  other  terminal  against  the  commutator  segments,  one 
at  a  time.  The  brush  and  the  terminal  should  not  touch  the 
same  segment.  The  armature  must  be  rotated  part  of  a  revolu- 
tion in  order  to  test  all  the  segments  individually.  The  testing 
magneto  should  be  turned  only  fast  enough  to  make  the  bell  ring. 
If  there  is  a  dead  segment,  the  bell  will  not  ring  when  the  testing 
terminal  is  in  contact  with  it.  It  should  ring  for  all  the  live 
segments.  The  dead  segment  indicates  a  broken  or  loose  con- 
nection between  it  and  the  armature.  More  rapid  turning  of 
the  testing  magneto  may  produce  a  pressure  sufficient  to  send 


TESTS   OF  IGNITION  SYSTEMS  22/ 

enough  current  across  a  break  whose  parts  are  onjy  an  extremely 
minute  distance  apart,  to  ring  the  bell. 

A  further  test  for  a  broken  commutator  connection  can  be 
made  with  a  galvanic  cell  (not  a  storage  cell)  or  some  other  source 
of  electric  energy  of  very  low  voltage  and  small  current  capacity. 
An  ammeter  suitable  for  measuring  very  small  currents  (milli- 
ammeter)  should  be  placed  in  the  circuit.  The  test  can  then  be 
made  as  before  by  connecting  one  terminal  of  the  cell  to  the  brush 
that  is  in  contact  with  the  commutator  and  the  other  terminal  to 
the  commutator  segments  in  turn.  The  amount  of  current  should 
be  noted  in  each  case.  If  the  broken  parts  are  pressed  but  very 
lightly  together,  the  current  for  the  corresponding  segment  will 
be  smaller  than  for  the  others.  Due  allowance  must  be  made 
for  the  dropping  off  of  the  current  capacity  of  the  cell  on  account 
of  polarization,  etc. 

Defective  insulation  between  the  different  turns  of  the  wire  of 
an  armature  coil  or  section  cannot  readily  be  determined  by  an 
electric  test  with  the  more  common  electric  instruments  unless 
the  armature  sections  or  coils  are  disconnected  from  the  com- 
mutator and  from  each  other.  Even  then  the  measurement  is 
one  of  electric  resistance  and  generally  requires  delicate  apparatus 
such  as  is  used  only  in  laboratories  and  electric  works. 

157.  Test  of  Direct-Current  Electro-Magnetic  Generator.  — 
Except  the  test  of  the  field  winding  for  magnetizing  the  soft 
steel  or  iron  magnet  cores  and  poles,  this  test  is  practically 
the  same  as  for  a  magneto  generator  as  given  in  the  preceding 
section. 

The  test  of  the  insulation  and  for  broken  wires  in  the  field  coil 
can  be  made  first  with  a  portable  magneto.  The  terminals  of 
the  field  winding  should  first  be  disconnected  from  the  other 
parts,  and  then  the  tests  made  between  the  terminals  of  the 
winding,  and  also  between  the  winding  and  the  metal  of  the 
generator. 

To  determine  whether  there  is  a  short  circuit  in  the  field  winding 
the  electric  resistance  of  the  coils  can  be  measured  and  compared 
with  what  it  was  when  the  coils  were  new.  The  old  and  new 
values  should  be  the  same,  after  corrections  have  been  made  for 


228  THE  GAS  ENGINE 

differences  of  temperature.  Laboratory  or  factory  instruments 
are  needed  for  the  latter  test. 

If  the  magnets  have  not  retained  enough  magnetism  to  cause  the 
generator  to  "pick  up"  and  produce  pressure  and  current,  they 
can  be  remagnetized  by  sending  a  current  from  a  battery  or  other 
source  through  the  field  winding.  This  will  remagnetize  the  field 
magnets.  Care  should  be  observed  to  have  sufficient  resistance 
in  the  magnetizing  circuit  while  doing  this,  in  order  to  prevent 
burning  out  the  field  winding  by  too  great  a  current.  An  incan- 
descent lamp,  or  two  or  more  lamps  in  parallel,  will  answer  if 
the  current  is  taken  from  a  commercial  lighting  circuit.  Only 
circuits  having  direct  current  can  be  directly  utilized  (without  a 
rectifier).  Water  resistance  will  answer  in  any  case.  Put  a 
little  acid  in  the  water  if  enough  current  will  not  flow  through 
pure  water.  The  electromagnets  are  generally  not  very  strong 
when  the  generator  is  not  running. 

158.  Tests  of  Shuttle- Wound  Electric  Generators.  —  Most  of 
the  oscillating  electric  generators  and  those  used  in  connection 
with  transformer  (induction)  coils  without  vibrators  (tremblers, 
interrupters)  belong  to  this  class.     The  tests  in  case  of  trouble 
are  of  the  same  nature  as  those  already  given,  but  simpler.     By 
following  such  parts  of  these  tests  as  apply  to  the  case  in  hand 
the  desired  results  can  be  obtained. 

When  one  terminal  of  the  single-coil  armature  winding  is  con- 
nected to  the  armature  shaft,  the  test  for  the  insulation  of  the 
winding  from  the  core  cannot  be  made  unless  this  connection  is 
opened  up  for  the  purpose. 

159.  Test  of  Shuttle- Wound  Oscillatory  Armature  Generators. 
—  A  permanent  magnet   (or  magnets)  is  used  on  this  type  of 

generator,  and  the  armature  is  generally  shuttle  wound  with  only 
one  coil.  Ordinarily  the  current  is  taken  off  either  by  a  pair  of 
insulated  collector  brushes  in  contact  with  a  corresponding  pair 
of  insulated  slip  rings,  or  one  end  of  the  armature  winding  is 
connected  to  the  armature  shaft,  which  has  metallic  connection 
to  the  frame  of  the  machine,  and  the  other  end  of  the  armature 
wire  is  connected  to  a  slip  ring  on  which  a  collector  brush  rests. 
When  the  armature  coil  is  connected  to  the  shaft  electrically,  the 


TESTS  OF  IGNITION  SYSTEMS  229 

test  of  the  insulation  between  the  winding  and  the  armature  core 
cannot  be  made  until  the  connection  to  the  shaft  is  broken 
(electrically).  Otherwise  the  test  is  the  same  in  general  as 
already  given  (see  §156),  except  that  there  is  only  one  ring 
or  a  pair  of  rings,  instead  of  several  segments  of  a  commutator. 

1 60.  Tests  of  High-Tension  Electric  Generators.  —  The  gen- 
erators of  this  class  are  so  varied  in  form  that  it  is  hardly  possible 
to  give  directions  that  will  apply  generally. 

The  tests  really  amount  to  a  combination  of  those  for  a  gen- 
erator, a  timer,  and  an  induction  coil  or  transformer  coil.  By 
combining  such  parts  of  these  tests  as  apply  to  a  particular 
machine,  a  complete  test  can  be  made. 

In  a  magneto  generator  whose  armature  is  stationary,  and 
whose  rotor  or  oscillator  is  a  permanent  magnet  without  any  wire 
winding,  the  sources  of  trouble  are  reduced  to  a  minimum.  The 
armature  test  for  it  is  similar,  but  simpler  than  when  the  arma- 
ture rotates.  The  test  for  magnetism  can  be  applied  after 
removing  the  magnet,  sometimes  without  removing  it. 


CHAPTER  XII. 
TESTS   FOR   AIR  AND  GAS   LEAKS   IN  MOTOR. 

161.  Examination  for  Leaks  while  the  Motor  is  Running  in 
Regular  Service.  —  To  detect  a  leak  at  the  spark  plug  or  other 
form  of  ignition  apparatus,  at  a  plug  or  other  stop  to  an  opening 
in  the  cylinder,  or  at  any  part  of  the  cylinder  that  is  accessible, 
put  a  plentiful  supply  of  the  cylinder  lubricating  oil  where  the 
examination  for  the  leak  is  to  be  made,  while  the  motor  is  running. 
Bubbles  will  appear  where  there  is  a  leak  if  it  is  not  so  great  as 
to  blow  off  the  oil.  The  oil  may  be  drawn  into  the  cylinder  to 
some  extent  if  the  leak  is  large. 

A  piston  leak  of  any  considerable  extent  allows  smoke  to  blow 
out  around  the  piston  during  the  impulse  stroke.  The  smoke 
is  especially  noticeable  when  the  combustion  mixture  is  over 
rich  or  there  is  too  abundant  lubrication.  It  may  be  necessary 
to  remove  part  of  an  enclosed  crank  case  to  see  the  end  of  the 
piston. 

A  cracked  or  porous  cylinder,  or  a  leaky  plug  in  the  cylinder 
wall  between  the  combustion  chamber  and  the  water  jacket, 
allows  gas  to  pass  from  the  combustion  chamber  into  the  jacket 
water  during  the  compression  and  the  impulse  strokes.  If  a 
cooling  tank  is  used,  bubbles  will  appear  where  the  hot  water 
flows  into  the  tank  at  the  end  of  the  pipe  that  carries  the  water 
from  the  motor  to  the  cooling  tank,  provided  that  the  opening 
of  the  pipe  is  entirely  submerged.  Bubbles  may  appear  here 
on  account  of  air  carried  into  the  jacket  space  with  the  cooling 
water.  A  chemical  analysis  will  determine  the  nature  of  the 
gas  in  the  bubbles.  Air  is  not  apt  to  be  carried  into  a  thermal 
circulating  system.  A  piece  of  glass  tube  interposed  in  the 
pipe  that  leads  from  the  water  jacket  affords  a  means  of  detect- 
ing bubbles  in  the  water.  The  glass  should  not  be  placed  so  near 
the  motor  as  to  show  steam  bubbles  that  have  not  had  time  to 

230 


TESTS  FOR  AIR  AND   GAS  LEAKS  IN  MOTOR         231 

condense.  A  glass  jar  filled  with  water  and  held  inverted  over 
the  outlet  of  the  submerged  pipe  with  most  of  the  jar  above  the 
water  level  can  be  used  to  determine  whether  the  bubbles  are 
steam. 

162.  Running  Test  for  a   Cracked   Cylinder,   Porous  Metal, 
Leaky  Plugs,  and  Leaks  into  the  Jacket  Space.  —  The  motor 
should  be  cool  at  the  beginning  of  the  test,  and  the  following 
preparations  should  be  made  before  starting  the  motor:     Dis- 
connect the  driving  mechanism  of  the   circulating  pump  and 
remove  the  pipe  connected  to  the  water  outlet  at  the  top  of  the 
jacket.     Fill  the  jacket  space  full  of  water  till  it  stands  level 
with  the  top  of  the  opening.     If  the  motor  is  small,  rotate  or 
crank  it  by  hand  and  note  whether  bubbles  rise  through  the  water. 
If  the  combustion  chamber  is  plugged  at  the  top,  it  can  generally 
be  observed  whether  the  bubbles,  if  any,  come  from  around  the 
plug. 

Start  the  motor  and  observe  as  before.  If  the  water  vibrates 
too  much  for  the  observation,  a  piece  of  glass  can  be  placed  over 
the  opening  with  the  water  high  enough  to  keep  it  in  contact 
with  the  glass.  Water  may  be  flowed  in  slowly  at  the  bottom 
of  the  jacket  and  allowed  to  escape  under  the  glass.  The  load 
on  the  motor  should  be  increased  to  the  full  capacity  of  the  motor 
without  much  delay.  Small  bubbles  of  air  will  soon  begin  to 
form  on  the  cylinder  wall  on  account  of  the  heat,  as  they  do  in 
a  glass  of  water  standing  for  some  time  on  a  warm  day,  and 
finally  steam  bubbles  will  form  unless  the  water  is  allowed  to 
flow  rapidly  enough  to  keep  it  below  the  boiling  temperature. 
The  air  and  steam  bubbles  must  not  be  taken  for  gas  from  cylinder 
leaks. 

In  an  oil-cooled  motor  the  test  is  the  same,  except  the  use  of 
oil  instead  of  water. 

163.  Hand-Compression  Tests  for  Cylinder  and  Piston  Leaks 
in  Small  Motors.  —  Cut  out  the  ignition,  open  the  pet-cocks  to 
the  combustion  chamber,  and  rotate  the  motor  to  see  that  it  moves 
freely.     Close  the  pet-cock  of  the  cylinder  to  be  tested.     Rotate 
again  till  the  compression  stroke  is  nearly  completed,  hold  the 
crank  shaft  in  this  position  and  note  whether  the  effort  necessary 


232  THE  GAS  ENGINE 

to  hold  it  grows  less  on  account  of  leakage.  The  crank  shaft 
may  also  be  worked  back  and  forth  to  move  the  piston  in  and 
out.  Note  whether  the  compression  resistance  decreases  during 
this  action.  If  the  compression  resistance  decreases  more 
rapidly  when  the  piston  is  moved  than  when  it  is  held  still  at 
nearly  the  completion  of  the  compression  stroke,  then  the  piston 
leaks  more  at  nearly  the  middle  of  its  stroke  than  at  and  near 
the  end  of  the  compression  stroke. 

In  case  the  compression  falls  rapidly,  the  valves  can  be  roughly 
tested  for  leaks  by  holding  a  piece  of  thin  cloth  or  tissue  paper 
over  the  end  of  the  exhaust  port  while  the  piston  is  held  stationary 
near  the  end  of  the  compression  stroke.  This  will  hardly  give 
definite  results  if  the  exhaust  pipe  has  leaks.  In  such  a  case  the 
exhaust  pipe  can  be  removed  and  the  paper  or  cloth  held  near 
the  opening,  or  the  caps  over  the  valves  can  be  removed  and  the 
valves  tested  by  putting  oil,  kerosene,  or  water  around  or  over 
them,  or  talc  powder  or  pulverized  soapstone  around  the  edges. 
A  piece  of  sheet  rubber  held  tightly  over  the  exhaust  opening,  as 
by  pressing  a  ring  against  it,  will  be  bulged  out  by  the  gas  that 
escapes  through  a  leak.  It  may  be  necessary  to  prevent  escape 
of  gas  around  the  stem  of  a  mechanically  operated  valve  by 
closing  the  crack  with  thick  grease. 

Leaks  from  the  cylinder  into  the  water  jacket  can  be  detected 
by  noting  whether  bubbles  escape  into  the  cooling  tank  or  rise 
through  the  water  in  the  jacket  when  the  pipe  is  disconnected 
from  the  top  of  the  jacket.  The  circulating  pump  should  not 
rotate  during  this  part  of  the  test.  (See  preceding  section.) 

Leaks  in  the  spark  plug,  pet -cock,  or  other  stopped  openings 
into  the  cylinder  can  be  detected  by  putting  oil  around  the 
parts. 

This  test  does  not  show  whether  the  piston  is  tight  when  well 
out  on  the  impulse  stroke  or  during  the  early  part  of  the  compres- 
sion stroke. 

164.  Compressed- Air  Test  for  Leaks.  —  The  air  pressure  for 
this  test  should  be  about  the  same  as  the  explosion  pressure  of 
the  motor.  A  pressure  of  350  pounds  per  square  inch  is  sufficient 
for  all  motors  except  those  in  which  air  alone  (and  residual  gases) 


TESTS  FOR  AIR  AND  GAS  LEAKS  IN  MOTOR         233 

is  compressed  in  the  combustion  space  before  the  fuel  is  admitted 
to  it,  as  in  the  case  of  one  type  of  oil  motor. 

The  connections  for  supplying  the  compressed  air  to  the  motor 
cylinder  can  be  made  by  removing  the  cylinder  pet -cock,  the  spark 
plug  or  other  ignition  apparatus  from  the  cylinder  and  then 
connecting  the  compressed-air  pipe  to 'the  opening. 

Set  the  motor  with  the  piston  in  position  to  begin  the  impulse 
stroke  and  lock  the  fly  wheel  so  that  it  cannot  rotate.  Put  on  the 
full  pressure  of  the  air  and  examine  for  leaks  by 'the  methods 
already  described  (see  preceding  section  and  others). 

Release  the  pressure  from  the  motor  cylinder  and  rotate  the 
crank  a  little  in  the  direction  that  it  runs.  Lock  the  fly  wheel 
again  and  apply  air  pressure  as  before,  but  the  full  pressure  need 
not  be  applied  if  the  piston  is  about  one-eighth  of  the  way  out  on 
its  stroke.  A  somewhat  less  air  pressure  will  do  for  this  position. 

Repeat  the  tests  through  the  full  stroke  of  the  piston. 

The  pressure  can  be  gradually  reduced  to  about  125  pounds  per 
square  inch  at  mid-stroke,  and  on  down  to  50  or  60  pounds  at  the 
end  of  the  stroke. 

It  is  generally  difficult  to  observe  directly  whether  the  piston 
leaks  on  a  standing  test  (motor  not  running).  The  elimination 
of  other  leaks  is  the  method  to  be  followed  in  such  a  case,  until 
it  is  known  that  there  is  no  leak  at  any  other  place. 

If  the  cylinder  has  been  detached  from  the  frame  of  the  motor 
and  is  small  enough  to  be  immersed  in  water,  the  piston  can  be 
held  in  by  a  wooden  block  and  bolts  while  the  air  pressure  is 
applied.  Bubbles  will  then  appear  at  every  leak.  The  piston 
can  be  set  at  different  positions  and  the  air  pressure  regulated 
accordingly  as  above. 

165.  Hydrostatic  Test  for  Piston  and  Cylinder  Leaks.  —  Water 
or  oil  pressure  can  be  applied  to  the  interior  of  the  cylinder  in  the 
same  manner  as  compressed  air,  as  just  described. 

In  applying  the  hydrostatic  test  the  pipe  should  be  disconnected 
from  the  bottom  of  the  jacket  space  and  the  water  or  oil  drained 
out.  Then  if  there  is  a  leak  from  the  cylinder  into  the  jacket 
space,  the  water  will  run  out  at  the  bottom  opening  of  the  jacket 
space.  The  caps  over  the  valves,  etc.,  should  be  removed  to 


234  THE  GAS  ENGINE 

allow  the  parts  which  may  leak  to  be  seen  as  far  as  possible. 
Piston  leaks  are  clearly  shown. 

Thin  oil  or  kerosene  may  be  used  instead  of  water.  The 
kerosene  will  pass  through  openings  that  will  retain  water  when 
the  parts  are  oily  or  greasy. 

The  joints  of  commercial  motors  are  seldom  tight  enough  to 
warrant  testing  in  the  above  manner  with  gasoline,  and  its  use 
cuts  the  oil  away  so  completely  from  the  cylinder  bore  and  piston 
rings  that  there  is  apt  to  be  cutting  between  them  afterward. 


CHAPTER  XIII. 
CLEANING  AND  MISCELLANEOUS. 

166.  Carbon  Deposit  in  the  Cylinder.  —  When  the  combustible 
mixture  is  too  rich,  or  when  an  unsuitable  quality  of  lubricating 
oil  is  used,  some  carbon  is  always  deposited  on  the  cylinder  walls 
and  piston  head.  The  rate  at  which  it  is  deposited  depends  on 
the  richness  of  the  combustible  mixture  and  the  amount  and 
unsuitability  of  the  oil  used  in  the  cylinder. 

The  carbon  is  deposited  in  two  forms.  Some  is  soft  like  soot 
and  some  hard  like  coke. 

The  soft  carbon  mingles  with  the  gummy  residue  of  the  lubri- 
cating oil  and  adheres  to  the  walls  of  the  combustion  chamber 
and  to  the  spark  plug.  If  the  lubricant  is  poor  and  insufficient 
in  quantity,  the  soft  carbon  is  deposited  to  some  extent  on  the 
walls  of  the  bore  of  the  cylinder  over  which  the  piston  passes. 
This  does  not  occur  with  good  oil  plentifully  applied. 

The  hard  carbon  forms  chiefly  at  the  hottest  parts  of  the  motor, 
and  especially  where  the  incoming  mixture  impinges  against  hot 
parts,  as  against  the  piston  of  a  small  motor.  It  always  forms 
with  an  uneven,  jagged  surface,  and  often  collects  in  lumps. 

The  carbon,  especially  the  hard  lumps,  may  become  heated 
to  a  glowing  temperature  when  the  motor  is  working  hard. 
When  thus  heated,  the  carbon  will  cause  back  firing  and  pre- 
ignition.  The  preignition  has  the  same  effect  as  advancing  the 
timer  or  igniter  too  far.  The  back  firing  is  caused  by  the  incom- 
ing charge  striking  the  incandescent  carbon.  The  incandescent 
carbon  will  often  cause  the  motor  to  continue  running  after  the 
regular  ignition  is  completely  cut  out. 

"Kicking"  when  starting  the  motor  soon  after  stopping  and 
while  it  is  still  hot  is  another  result  of  hot  carbon  deposit. 

The  soft,  gummy  mixture  of  carbon  and  oil  residue  between 
the  piston  and  the  cylinder  wall  increases  the  frictional  resistance 

235 


236  THE  GAS  ENGINE 

of  the  motor,  and  thus  reduces  its  effective  power,  at  the  same 
time  increasing  its  tendency  to  heat,  both  on  account  of  the 
increased  frictional  resistance  and  the  larger  or  more  frequent 
charges  of  combustible  that  must  be  used  to  overcome  the  friction. 
It  also  works  around  and  under  the  piston  rings  so  as  to  counter- 
act their  elastic  action  and  prevent  close  conformation  to  the 
cylinder  bore,  thus  causing  leakage  around  the  piston  and  loss  of 
power. 

A  badly  gummed  piston  offers  considerable  resistance  to  the 
rotation  of  the  motor.  The  ease  with  which  a  small  motor  can 
be  rotated  by  hand  is  an  indication  of  the  condition  of  cleanliness 
and  lubrication  of  the  piston. 

The  carbon  and  oil  sometimes  collect  on  the  stem  of  the 
exhaust  valve  and  become  baked  so  as  to  form  a  hard  coating 
that  causes  the  stem  to  bind  in  its  guide.  Except  in  the  case  of 
continued  back  firing,  the  inlet -valve  stem  does  not  become 
carbon  coated  to  an  appreciable  extent. 

A  sudden  loss  of  compression  and  power  in  the  motor  is  some- 
times caused  by  a 'flake  of  the  hard  carbon  detaching  itself  and 
lodging  under  one  of  the  valves,  generally  the  exhaust  valve. 
The  effect  of  this  is  the  more  noticeable  the  fewer  the  number 
of  combustion  chambers  in  the  motor. 

Scoring  of  the  piston  and  cylinder  may  be  caused  by  a  loose 
flake  of  the  carbon  getting  between  them.  This  is  very  unusual 
when  the  lubricating  oil  is  of  the  right  quality  and  enough  is 
applied. 

A  liberal  supply  of  suitable  lubricating  oil  while  the  motor  is 
running  will  generally  remove  the  carbon  deposit  from  the  valve 
stem  and  from  between  the  piston  and  cylinder.  After  the  motor 
has  been  stopped  and  cooled  so  as  not  to  be  very  hot,  kerosene 
can  be  applied  for  the  same  purpose,  or  gasoline  may  be  used  on 
an  entirely  cool  motor.  Kerosene  left  standing  in  the  cylinder 
will  dissolve  the  gum  in  a  few  hours.  Slow  rotation  of  the  motor 
helps  to  cut  out  the  deposit  rapidly.  The  motor  should  be  well 
lubricated  before  starting  it  after  cleaning  the  cylinder  with 
kerosene,  and  especially  after  using  gasoline  for  cleaning. 

Scraping  and  rubbing  is  the  only  method  of  removing  the  hard 


CLEANING  AND  MISCELLANEOUS  237 

carbon  deposit  from  the  combustion  chamber  walls  and  piston 
head.  It  cannot  be  dissolved  by  anything  that  can  be  safely  or 
economically  used  in  the  cylinder. 

167.  Cleaning  the  Spark  Plug.  —  When  the  insulation  of  a 
spark  plug  is  covered  with  a  coating  of  carbon  and  oil,  it  can 
generally  be  cleaned,  if  accessible,  with  gasoline  and  a  bristle 
brush  or  a  piece  of  cloth  and  a  string  for  getting  into  the  angles. 
A  wire  brush  should  not  be  used,  for  it  is  apt  to  scratch  and 
roughen  the  insulation  so  that  it  will  gather  and  hold  dirt  and  be 
impossible  to  clean  again.     Mica  insulation  should  not  be  scraped 
with  a  knife  under  any  circumstances,  and  the  use  of  a  knife 
must  be  with  care  even  on  porcelain.     Foreign  matter  on  the 
metallic  points  is  not  harmful  except  when  it  is  between  the 
ignition  points  or  contacts. 

Porcelain  insulation  can  sometimes  be  successfully  removed 
for  cleaning  it  if  the  plug  is  not  too  old  in  service.  The  writer's 
experience  in  this  direction  has  been  that  the  porcelain  generally 
sticks  and  binds  so  tight  that  it  is  necessary  to  break  it  in  order 
to  remove  it  from  the  rest  of  the  plug.  A  new  porcelain  can  be 
put  in  its  place,  which  is  better  and  not  expensive. 

1 68.  Pitting  and  Warping  of  the  Exhaust  Valve.  —  When  the 
ignition  is  late  or  the  mixture  is  over  rich,  the  flame  is  still  burning 
in  the  cylinder  when  the  exhaust  valve  is  opened.     The  flame  then 
passes  out  into  the  exhaust  passages  and  heats  the  exhaust  valve 
to  a  high  temperature.     The  high  temperature  has  a  tendency 
to  warp  the  valve,  whatever  its  material.     The  combined  heating 
and  erosive  action  of  the  escaping  burning  gases  often  produce 
small  pits  and  shallow  cavities  in  the  part  of  the  valve  that  rests 
on  the  seat  when  the  valve  is  closed.    Forged-steel  valves  are  more 
subject  to  pitting  than  cast-iron  ones. 

Pitting  is  apt  to  cause  leakage  at  the  valve,  although  a  valve 
may  sometimes  be  very  much  pitted  and  still  remain  tight.  The 
pits  are  more  or  less  circular  in  shape,  and  one  may  form  in  the 
middle  of  the  bearing  surface  without  extending  to  either  edge,  or 
in  one  side  of  the  bearing  surface  without  extending  across  it. 
Warping  is  certain  to  cause  leakage  and  loss  of  power. 

The  remedy  is  to  regrind  the  valve. 


238  THE  GAS  ENGINE 

169.  Regrinding  a  Leaky  or  a  Pitted  Valve.  —  Mix  a  finely 
granulated  or  pulverized  abrasive,  such  as  emery,  ground  glass, 
etc.,  with  vaseline  or  grease.  Stop  the  port  with  a  piece  of  cloth 
or  waste,  if  possible.  It  may  be  necessary  to  remove  the  valve  to 
do  this. 

Place  a  small  amount  of  the  grinding  mixture  on  the  bearing 
surface  of  the  valve.  Put  the  valve  back  in  place  (if  it  has  been 
removed)  and  rotate  it  back  and  forth  with  an  oscillatory  motion 
a  few  times  while  applying  a  slight  pressure  to  hold  it  against  its 
seat.  The  movements  in  one  direction  may  always  be  a  little 
less  than  in  the  other,  so  that  the  valve  is  slowly  turned  around  as 
well  as  oscillated.  Lift  the  valve  slightly  from  its  seat  frequently 
to  allow  the  abrasive  to  get  between  the  bearing  surfaces.  A 
light  spring  placed  under  the  valve  is  convenient  for  lifting  it 
when  the  pressure  is  removed.  It  is  not  advisable  to  rotate  the 
valve  through  complete  revolutions  in  either  direction,  for  such  a 
movement  is  apt  to  make  scratches  completely  around  the  bearing 
surfaces.  An  exception  to  this  may  be  a  valve  that  is  in  extremely 
bad  condition  from  pitting  or  warping,  etc.  In  such  a  case  the 
grinding  may  be  more  rapid  at  first  by  rotating  several  times  first 
in  one  direction  and  then  in  the  other,  lifting  the  valve  from  its 
seat  at  each  reversal  of  the  motion. 

Remove  the  valve  and  examine  it  frequently  to  see  how  the 
grinding  is  progressing.  The  bearing  surfaces  take  on  the  same 
dull  appearance  all  the  way  around  when  the  grinding  becomes 
uniform  and  they  are  nearly  or  quite  fitted  together. 

Badly  pitted  or  warped  valves  can  be  ground  to  advantage  in 
a  lathe  or  grinding  machine  with  an  emery  wheel  (or  other 
abrasive  wheel),  then  finished  in  place  as  above. 

If  the  valve  is  oscillated  in  the  same  position  always,  the  sur- 
faces may  become  ground  off  more  in  some  places  than  in  others. 
The  valve  will  then  fit  in  some  positions  but  not  in  others. 

An  abrasive  two  or  three  grades  coarser  than  flour  emery  may 
be  used  at  first,  and  a  finer  grade  to  finish.  The  coarse  grade 
should  be  removed  before  putting  on  the  fine. 

Great  care  should  oe  exercised  to  prevent  the  aorasive  from 
getting  into  the  ports  of  the  cylinder,  especially  the  inlet  port. 


CLEANING  AND   MISCELLANEOUS  239 

The  parts  should  be  cleaned  with  extreme  care  aj  the  completion 
of  grinding.  Any  abrasive  that  enters  the  cylinder  will  cut  and 
score  it,  and  cause  rapid  wear  and  piston  leaks. 

170.  Running   the   Motor  with   a    Disabled   Valve   or  Valve 
Spring.  —  If  a  valve  of  one  of  the  cylinders  of  a  motor  with  more 
than  one  combustion  chamber  is  broken  or  disabled,  or  the  valve 
spring  useless,  the  motor  can  be  run  in  a  disabled  condition  by 
permanently  closing  the  inlet  port  of  the  combustion  chamber 
whose  valve  is  disabled.     It  is  generally  advisable  to  close  the 
exhaust  port  also  to  prevent  scale  and  carbon  from  being  drawn 
into  the  cylinder  through  it. 

The  port  can  be  closed  by  putting  a  piece  of  sheet  metal  or 
strong  gasket  material,  in  the  form  of  a  blank  gasket,  in  place 
of  the  regular  gasket  in  the  joint  of  the  connection  near  the  motor. 
Or,  if  the  valve  stem  is  the  part  broken,  the  valve  can  be  clamped 
down  against  its  seat  by  removing  the  cap  from  over  the  valve  and 
putting  a  piece  of  wood  on  the  valve  and  then  clamping  it  down 
by  replacing  the  cap.  When  the  inlet  valve  is  automatic  and 
located  opposite  the  exhaust  valve  (so  that  the  two  open  toward 
each  other)  the  block  can  be  placed  between  them.  In  any 
method  of  blocking  down  a  mechanically  operated  valve,  the 
means  of  lifting  it  should  be  removed  before  blocking  it  down. 

The  compression  of  the  disabled  cylinder  can  be  relieved  by 
removing  the  spark  plug,  if  thought  necessary. 

A  broken  coiled  valve  spring  can  sometimes  be  kept  in  use  by 
placing  a  washer-shaped  piece  of  stiff  material  around  the  valve 
stem  and  between  the  broken  parts  of  the  spring.  A  round, 
flanged  (shallow  cup  shaped)  piece  with  a  hole  in  the  center 
may  serve  better  if  the  coil  of  the  spring  is  of  large  diameter  in 
comparison  with  that  of  the  valve  stem;  or  a  flat  disk  of  metal 
slitted  radially  from  the  edge  inward  a  short  distance  at  several 
places,  and  part  of  the  strips  between  the  slits  bent  up  and  the 
others  down  so  that  they  will  fit  over  the  outside  of  the  broken 
parts  of  the  spring,  may  answer  better. 

171.  Carbureter   Repairs.     "  Water-logged  "  Float.     Grinding 
a  Needle  Valve.  —  A  hole  in  the  hollow  metal  float  of  a  float-feed 
carbureter  may  let  gasoline  enter  the  float  if  the  hole  is  below  the 


240  THE  GAS  ENGINE 

level  of  the  gasoline.  The  increased  heaviness  of  the  float  on 
this  account  allows  the  gasoline  to  rise  higher  in  the  reservoir 
than  it  should  and  thus  causes  too  rich  a  mixture.  To  repair  it, 

Take  the  float  out  of  the  carbureter  and  place  it  in  hot  water 
to  locate  the  hole  by  the  bubbles  that  come  from  it.  Make  a 
small  hole  in  the  float,  dry  it  and  drive  out  the  gasoline  by  gentle 
heating.  Solder  the  leak  and  test  it  by  blowing  into  the  small 
hole  just  made.  Let  the  float  cool  completely  and  solder  the 
small  hole  quickly  with  a  soldering  iron  so  as  to  heat  the  float  as 
little  as  possible. 

If  a  cork  float  becomes  "water-logged"  or  heavy,  remove  it 
and  dry  by  gentle  heating,  then  varnish  it  again. 

If  the  needle  valve  of  the  float  becomes  leaky,  press  it  down 
on  its  seat  and  rotate  it,  being  careful  not  to  bend  it.  If  this  does 
not  stop  the  leak,  grind  it  in  with  very  fine  abrasive  (as  emery) 
mixed  with  vaseline  or  grease.  Press  lightly  on  the  valve  when 
rotating  it  to  grind,  and  lift  it  from  its  seat  frequently  to  allow  the 
abrasive  to  get  between  the  valve  and  its  seat.  Clean  off  all  of 
the  abrasive  carefully  when  the  grinding  is  finished. 

172.  Removing  Frost  and  Ice  from  the  Carbureter.  —  The 
frost  is  collected  from  the  air  and  the  ice  may  come  from  water 
which  splashes  in  or  is  drawn  in  and  freezes.     Both  obstruct  the 
passage  and  may  hinder  the  operation  of  the  throttle. 

The  ice  will  generally  thaw  out  if  the  motor  is  stopped  for  a 
short  time.  If  it  does  not,  lift  one  of  the  mixture  inlet  valves  of  the 
motor  slightly  and  crank  the  motor  while  the  valve  is  held  open; 
or  run  the  motor  by  its  own  power  should  there  be  more  than  one 
combustion  chamber.  Holding  the  inlet  valve  open  will  allow 
the  heated  gas  from  the  cylinder  to  be  forced  back  into  the  inlet 
passage  and  the  ice  will  be  melted  by  it. 

Hot  water  from  the  cooling  system  can  be  poured  on  to  melt 
the  ice. 

173.  Pipe  Stoppages  by  Gaskets  and  Loose  Hose  Linings.  - 
If  a  gasket  is  of  soft  material,  it  may  be  squeezed  out  into  the 
passage  so  as  to  partly  or  completely  stop  it.     Such  materials  as 
leather,  rubber  composition,  and  lead  (the  metal)  will  .act  this  way, 
especially  if  the  leather  or  rubber  becomes  soaked  and  covered 


CLEANING  AND  MISCELLANEOUS  241 

with  water  and  oil.  A  heavy  pressure  on  a  lead  gasket  will 
invariably  squeeze  it  out  from  between  the  surfaces.  The  best 
remedy  is  not  to  use  such  materials  where  the  conditions  are  of 
this  nature. 

The  lining  of  rubber  hose  such  as  is  used  for  the  cooling  water 
not  infrequently  becomes  partly  detatched  from  the  fabric  of  the 
hose.  It  will  sometimes  act  as  a  check  valve  or  a  flap  valve, 
especially  if  the  loose  part  is  just  where  the  hose  fits  over  a  coup- 
ling into  which  the  water  passes  from  the  hose.  A  loose  piece 
of  the  hose  lining  will  lodge  at  such  a  place  and  close  the  passage. 

174.  A  cracked  cylinder  or  cylinder  head  is  very  apt  to  be  the 
result  of  overheating  on  account  of  failure  of  the  cooling  water  or 
cooling  oil  to  circulate.     Lack  of  a  full  supply  of  cooling  water 
or  cooling  oil  will  produce  the  same  result.     Both  water-cooled 
and  oil-cooled  motors  will  withstand  a  great  deal  of  this  kind  of 
abuse  without  cracking,  however,  when  properly  made  of  suitable 
material. 

A  crack  in  the  cylinder  or  the  head  may  be  due  to  initial 
stresses  in  the  casting  on  account  of  the  design  or  the  method  of 
cooling  the  casting  in  the  mold  (or  out  of  it)  just  after  it  is  poured. 

175.  Leaky    Piston.     Scored    Cylinder.  —  A    leaky    piston    is 
almost  invariably  due  to  improperly  fitted,  worn,   grooved,  or 
broken  piston  rings  or  a  scored   (cut,  abraded)  cylinder  bore. 
Very  infrequently  it  is  on  account  of  a  cracked  piston,  the  crack 
generally  being  in  the  head  end  (the  end  next  to  the  combustion 
chamber  in  a  single-acting  motor). 

The  best  method  of  dealing  with  grooved,  cut,  or  badly  worn 
piston  rings  is  to  replace  them  with  new  ones.  An  improperly 
fitted  piston  ring  or  one  slightly  worn  so  that,  in  either  case,  the 
bearing  against  the  cylinder  bore  is  only  part  way  around,  can  be 
improved  by  peening  it  on  the  inner  surface  by  striking  lightly 
with  the  ball  peen  of  hammer  while  the  outside  of  the  ring  rests 
on  a  smooth  anvil.  This  will  expand  the  ring  and  cause  it  to 
bear  out  against  the  cylinder  harder  and  therefore  to  fit  to  it  more 
closely,  if  the  peening  is  done  properly.  Most  of  the  peening 
should  be  done  opposite  the  places  on  the  periphery  that  have 
been  worn  bright  by  rubbing  against  the  cylinder.  The  peening 


242  THE  GAS  ENGINE 

must  be  done  with  great  care,  since  the  rings  are  made  of  cast 
iron  (except  in  possible  unusual  cases). 

If  the  rings  are  loose  sidewise  in  the  grooves  of  the  piston,  it  is 
advisable  to  get  new  ones.  If  a  new  one  is  very  slightly  too  wide 
for  the  groove,  it  can  be  ground  down  on  the  sides  by  rubbing  it 
on  a  piece  of  emery  (or  other  abrasive)  cloth  or  paper  lying  on 
a  truly  flat  surface. 

A  piston  ring  that  is  loose  sidewise  sometimes  makes  a  sharp 
click  when  the  motor  is  running.  This  is  more  apt  to  occur  if  the 
cylinder  is  not  well  lubricated. 

Before  placing  the  rings  on  a  piston,  it  should  be  noticed 
whether  the  pin  or  other  device  for  preventing  each  ring  from 
turning  around  in  its  groove  is  in  place.  The  rings  should  be 
held  by  the  pins  or  stops  so  that  the  cuts  across  them  do  not  come 
near  each  other. 

A  piston  ring  can  be  removed  by  lifting  one  of  the  ends  at  the 
cross  cut  with  a  piece  of  soft  metal,  such  as  the  flattened  end  of 
a  copper  wire,  and  then  twisting  the  ring  around  while  pressing 
it  sidewise,  still  keeping  the  wire  under  it,  or  allowing  the  ring  to 
ride  on  top  of  the  pin  or  stop  for  preventing  its  rotation  when  in 
place.  The  ring  can  be  kept  from  snapping  back  into  the  groove 
while  removing  it,  by  placing  small  pieces  of  wood,  leather,  wood 
fiber,  etc.,  under  its  end  in  the  groove  after  lifting  the  end  and 
while  twisting  the  ring  around.  The  ring  should  not  be  sprung 
open  any  farther  than  is  necessary  to  remove  it.  Rings  of  cast 
iron  are  easily  broken  on  account  of  the  brittleness  of  the  metal. 

Putting  a  piston  ring  in  place  is  far  less  difficult  than  removing 
it,  but  the  same  care  must  be  observed  not  to  open  and  break  it. 
To  prevent  its  snapping  into  a  groove  that  is  to.be  passed  over, 
it  can  be  kept  very  slightly  crooked  on  the  piston. 

The  piston,  if  of  the  trunk  type,  can  be  tested  for  a  crack  by 
removing  it  from  the  cylinder,  placing  it  with  the  open  end  up,  and 
then  pouring  gasoline  or  naphtha  inside.  The  liquid  will  almost 
instantly  appear  on  the  outside  if  there  is  even  a  very  minute  crack. 
Immersing  it  in  gasoline  will  also  show  the  crack  or  pore. 

The  only  way  of  repairing  a  badly  cut  or  grooved  cylinder  is 
to  rebore  it.  If  the  wall  is  thick  enough  to  allow  it,  the  bore  may 


CLEANING  AND  MISCELLANEOUS  243 

be  made  large  enough  to  put  in  a  lining  bored  to  correspond  with 
the  diameter  of  the  piston.  Otherwise  a  new  piston  will  be 
required. 

176.  Care  and  Handling  of  Combustible  Liquids.  Removing 
Water.  —  Gasoline  and  naphtha  vaporize  rapidly  when  exposed 
to  the  air.  The  vapor  is  heavier  than  air,  and  therefore  settles 
to  the  floor  of  a  room,  the  bottom  of  a  boat,  etc.  The  mixture 
at  the  floor  soon  becomes  rich  enough  to  ignite  readily. 

Vents  to  remove  the  vapor  must  be  at  the  bottom  of  the  enclosed 
space.  Openings  under  doors  and  through  the  wall  to  the 
atmosphere  will  generally  allow  the  vapor  to  escape,  but  in  very 
quiet,  damp  or  humid  weather  the  circulation  of  air  (and  vapor) 
is  apt  to  be  so  slight  as  to  leave  them  practically  stagnant.  The 
same  is  true  of  venting  through  flues  that  lead  up  from  openings 
at  the  floor.  Forced  ventilation  with  a  blower  or  a  hot  steam 
coil  in  the  flue  is  effective  and  reliable. 

The  safest  storage  of  inflammable  liquids  is  in  an  underground 
tank,  and  the  safest  way  to  remove  them  from  the  tank  is  with  a 
suction  pump  so  constructed  that  any  leakage  of  the  valves  and 
other  parts  will  allow  the  liquid  to  drain  back  into  the  tank. 

Gasoline  and  other  volatile  combustible  liquids  evaporate  rap- 
idly from  a  closed  wooden  barrel.  This  is  especially  true  if  the 
barrel  is  exposed  to  the  sun.  Covering  the  barrel  with  a  heavy, 
damp  cloth  or  blanket  prevents  the  evaporation  to  some  extent. 

Gasoline,  etc.,  should  not  be  allowed  to  drain  into  sewers.  It 
is  liable  to  be  the  cause  of -explosions  in  them  which  will  blow 
manhole  covers  high  in  the  air  and  possibly  wreck  the  sewers. 

Water  can  be  removed  from  gasoline  and  other  volatile  products 
of  petroleum  either  by  filtering  (straining)  or  allowing  the  water 
to  settle  to  the  bottom.  A  water  trap,  which  may  be  something 
like  those  used  in  plumbing,  but  larger  and  well  out  of  the  current 
of  the  liquid,  will  remove  the  water  if  the  flow  past  the  trap  is 
slow.  Chamois  skin  strains  out  water  and  dirt  most  effectively, 
but  the  process  is  apt  to  be  slow.  Felt,  linen  and  cloth  do  well, 
but  the  material  should  be  such  as  will  not  give  off  lint  appreciably. 
The  lint  will  clog  the  small  passages  of  the  carbureter  and 
atomizer. 


244  THE   GAS  ENGINE 

There  should  be  as  few  sources  of  accidental  ignition  of  in- 
flammable vapor  in  a  place  where  volatile  combustibles  are 
present  as  possible.  Some  of  the  things  that  will  cause  ignition 
are:  a  spark  from  a  nail  in  one's  shoe  rubbing  over  or  striking 
against  a  cement  or  stone  floor;  a  spark  from  metal  tools  striking 
together  or  on  a  cement  floor;  an  electric  spark  at  a  lamp  switch 
or  at  the  brushes  of  a  generator  or  motor;  electric  sparks  from  a 
running  belt;  a  lighted  match,  lamp,  or  candle;  a  leak  in  the 
exhaust  connections  of  an  internal -combustion  motor. 

The  gasoline  tank,  or  a  joint  in  its  connections,  should  never  be 
located  so  that  leakage  or  drip  can  fall  on  or  otherwise  reach  the 
exhaust  pipe,  muffler,  or  other  highly  heated  parts. 

In  a  launch  or  boat  it  is  advisable  to  give  the  fuel  tank  sea 
drainage.  This  can  be  done  by  placing  the  tank  in  a  water-tight 
compartment  with  small  openings  through  the  hull  to  the  sea. 
The  tank  may  be  either  submerged  or  above  the  water  level. 
The  connections  should  have  no  joints  from  which  leakage  can 
drain  into  the  boat.  In  no  case  should  joints  be  hidden  from 
view  or  inaccessible.  It  is  best  to  have  a  solid  length  of  pipe  from 
the  tank  to  the  carbureter.  Running  the  fuel  pipe  line  outside  of 
the  hull  is  a  safe  precaution  frequently  found  in  practice.  The 
carbureter  should  have  overboard  drainage,  or  something  should 
be  provided  to  catch  any  possible  drip  from  it. 


CHAPTER  XIV. 

INDICATOR    CARDS    FROM   PRACTICE.* 

177.  The  indicator  diagram  of  an  internal -combustion  motor 
with  reciprocating  piston  is  obtained  in  the  same  general  manner 
as  for  a  similar  type  of  steam  engine.  The  diagram  is  a  record, 
more  or  less  accurate,  of  the  pressure  in  the  motor  cylinder 
during  the  operation  of  the  motor  through  one  cycle. 

The  form  of  the  diagram  and  the  time  required  for  the 
tracing  point,  ray  of  light,  or  other  recording  device  to  trace  it 
on  the  card,  measured  in  strokes  of  the  piston,  depend  on  the 
cycle  of  the  motor.  Four  strokes  of  the  piston,  corresponding  to 
two  revolutions  of  the  crank  shaft  (except  in  unusual  cases),  must 
be  made  to  secure  a  complete  card  of  a  four-cycle  motor.  A  two- 
cycle  motor  gives  a  complete  card  of  the  combustion  cylinder 
during  two  strokes  of  the  piston,  corresponding  to  one  revolution 
of  the  crank  shaft. 

When  taking  the  card,  the  connections  between  the  indicator 
and  the  motor  combustion  chamber  should  be  as  short  and  direct 
as  possible,  and  as  small  in  cross-section  as  will  allow  the  pressure 
of  the  combustion  chamber  to  be  transmitted  to  the  piston  of  the 
indicator  without  appreciable  reduction  by  frictional  resistance 
to  the  flow  of  the  gas  through  the  connecting  passage.  It  is 
more  important  in  the  internal-combustion  motor  that  the  volume 
of  the  space  added  to  the  combustion  chamber  by  the  indicator 
and  its  connections  shall  be  small  in  comparison  to  the  volume 
of  the  motor  cylinder  than  it  is  for  a  steam  engine. 

The  increase  of  the  volume  of  the  compression  space  of  a  motor 
on  account  of  connecting  the  indicator  to  it  reduces  the  pressure 
of  compression  and  consequently  that  of  combustion  or  explosion, 

*  For  method  of  obtaining  mean  effective  pressure  from  an  indicator  card 
see  chapter  on  Pressure -Volume  diagrams. 

245 


246 


THE   GAS  ENGINE 


as  well  as  the  efficiency  of  the  transformation  of  the  heat  energy 
of  the  gas  into  mechanical  power. 

An  indicator  card  from  a  four-cycle  motor  operating  on  gas 
from  a   suction   producer  is  accurately  reproduced  in  Fig.  77. 


FIG.  77, 


Stop  Line 


FIG.  78. 

The  atmospheric  pressure  line  is  only  partly  shown  in  order  to 
leave  the  diagram  as  clear  as  possible.  The  arrows  indicate  the 
direction  of  motion  of  the  tracing  point  over  the  card  when  making 
the  lines  of  the  diagram. 

The  suction  stroke  begins  at  A  and  ends  at  B.  Compression 
begins  at  B  and  continues  to  the  neighborhood  of  C,  wliere  ignition 
occurs,  and  the  pressure  rises  rapidly  to  D,  while  the  motor  piston 


INDICATOR  CARDS  FROM  PRACTICE  247 

makes  but  little  movement.  The  impulse  stroke*  begins  at  some 
point  between  C  and  D.  The  point  of  ignition  and  that  where 
the  impulse  stroke  begins  cannot  be  accurately  determined  on  the 
card.  Combustion  is  well  completed  at  the  reversal  of  the  curve 
after  it  begins  to  drop  on  the  impulse  stroke.  Expansion  of  the 
gases  of  combustion  continues  in  the  tightly  closed  cylinder  till 
the  exhaust  valve  opens  at  the  point  near  E,  where  the  expansion 
line  again  reverses  its  curvature.  The  impulse  stroke  is  com- 
pleted at  the  point  farthest  to  the  right  of  and  just  below  E. 
The  exhaust  stroke  then  begins  and  continues  along  the  upper 
and  nearly  horizontal  line  that  crosses  the  compression  line  at  F 
and  terminates  at  the  starting  point  A.  The  junction  of  the 
compression  line  with  the  combustion  curve  at  about  the  point  C 
is  unusually  smooth  in  this  diagram  and  therefore  makes  the  point 
C  difficult  to  locate  accurately.  The  ignition  occurs  slightly 
before  the  completion  of  the  compression  stroke. 

The  pumping  action  necessary  to  draw  the  air  into  the  fuel  bed 
of  the  gas  producer,  and  the  gas  there  formed,  from  the  producer 
and  through  the  scrubber  and  purifier  to  the  motor,  causes  the 
suction  line  of  this  card  to  fall  farther  below  the  atmospheric 
pressure  line  than  for  a  properly  designed  and  installed  motor 
using  gas  from  pressure  mains,  volatile  fuel  through  a  carbureter, 
or  oil  injected  into  the  combustion  chamber  or  into  a  vaporizer. 

The  area  of  the  upper  loop  CDEFC  of  the  indicator  card 
represents  the  energy  that  acts  to  drive  the  piston  of  the  rnotor. 
It  may  be  called  the  positive  area.  The  area  of  the  lower  loop 
ABFA  represents  energy  that  acts  to  retard  the  motion  of  the 
piston,  and  may  be  called  the  negative  area.  The  difference  of 
the  two  areas  (positive  —  negative)  therefore  represents  the 
energy  that  is  delivered  to  the  piston  during  a  complete  cycle  of 
the  motor,  dealing  with  one  combustion  chamber  only,  and  may 
be  called  the  net  area  or  effective  area  of  the  indicator  card.  To 
put  this  in  a  more  convenient  form  it  may  be  written 

Area  CDEFC  =  positive  or  impulse  energy; 

Area  ABFA  —  negative,  retarding,  or  pumping  energy; 

Area  (CDEFC  -  ABFA)  =  net  driving  or  effective  energy. 


248  THE  GAS  ENGINE 

The  net  area  of  the  card  can  be  found  with  a  planimeter  by 
starting  at  any  point  on  the  line  and  tracing  continuously  over 
the  boundaries  of  both  loops  in  the  direction  of  the  arrows  back 
to  the  starting  point.  The  planimeter  will  record  positively  for 
the  upper  loop  and  negatively  for  the  lower  loop.  The  net 
record  will  be  the  difference  of  the  areas  of  the  two  loops. 

The  upper  loop  CDEFC  is  often  referred  to  as  the  impulse 
diagram,  impulse  card,  or  simply  the  indicator  card  of  the  motor. 
The  latter  usage  has  probably  arisen  from  the  fact  that  the  area 
of  the  lower  loop  is  generally  so  small  in  cards  from  motors  that 
do  not  draw  their  fuel  through  a  suction  producer,  that  it  is 
impossible  to  measure  its  area  with  any  degree  of  accuracy  even 
when  drawn  with  a  sharp  metallic  tracing  point,  when  the  com- 
plete double  loop  is  traced  continuously,  as  in  Fig.  77. 

When  the  lines  enclosing  the  area  of  the  lower  loop  lie  so  close 
together  as  to  make  it  impossible  to  determine  its  area  with  an 
error  less  than  50  per  cent  of  its  own  area,  its  omission  altogether 
from  the  complete  card  will  not  generally  introduce  an  error  as 
great  in  actual  area  as  that  of  determining  the  area  of  the  upper 
loop. 

But  since  the  area  of  the  lower  loop  represents  negative  work 
done  by  the  motor,  it  is  desirable  to  reduce  the  value  of  this  area 
to  as  small  an  amount  as  possible  that  is  consistent  with  other 
factors  to  be  considered. 

In  order  to  obtain  a  separate  indicator  card  that  will  clearly 
show  the  characteristics  of  the  lower  loop,  a  weak  spring  is  used 
in  the  indicator  (in  connection  with  a  stop  that  will  prevent  the 
indicator  piston  and  tracing  point  from  being  thrown  too  high 
if  the  instrument  is  not  so  constructed  as  to  limit  the  motion  of 
its  piston  and  tracing  point  within  a  safe  range  without  a  stop). 
The  card  thus  obtained  shows  the  lower  part  of  the  diagram,  as 
of  that  in  Fig.  77,  on  an  enlarged  vertical  scale,  the  upper 
part  of  the  complete  diagram  being  cut  off  by  a  line  traced  parallel 
to  the  atmospheric  line  by  the  tracing  point  of  the  indicator,  while 
its  moving  parts  are  held  at  the  limit  of  their  motion  caused  by 
the  pressure  of  the  gases  in  the  cylinder. 

Such    an    indicator  card    is  shown   in   Fig.    78,   which    is   a 


INDICATOR  CARDS    FROM  PRACTICE  249 

vertical  enlargement  of  the  lower  part  of  Fig.  77.  It  may 
be  referred  to  as  a  low-spring  card,  pumping  card,  or  pump 
card. 

Many  of  the  causes  that  effect  changes  in  the  form  and  area 
of  the  impulse  card  are  different  from  those  that  produce  similar 
variations  in  the  pumping  card.  For  this  reason,  as  well  as  on 
account  of  the  contracted  form  of  the  pumping  card  when  taken 
in  connection  with  the  impulse  card,  it  is  customary  to  take  a 
separate  low-spring  indicator  card  of  the  form  just  described  to 
show  the  pumping  action.  A  card  of  this  kind  is  also  very 
useful  for  examining  the  valve  action. 

The  mean  effective  pressure  of  either  card  can  be  found  in  the 
usual  manner,  by  dividing  its  area  (square  inches)  by  its  length 
(inches)  and  then  multiplying  by  the  value  of  the  indicator  spring 
(pounds  per  inch  of  height  of  the  indicator  card). 

The  remainder  obtained  by  subtracting  the  mean  effective 
pressure  of  the  pumping  card  from  that  of  the  impulse  card, 
both  reduced  to  the  same  scale,  represents  the  net  mean  pres- 
sure that  is  effective  in  driving  the  motor  piston  when  the  com- 
plete cycle  is  taken  into  consideration. 

The  indicated  horsepower  of  a  single-cylinder,  single-acting 
motor  or  of  one  combustion  chamber  of  a  multi-cylinder  or 
double-acting  motor  is  obtained  by  multiplying  together  the  net 
mean  effective  pressure,  the  cross-sectional  area  of  the  clear 
space  in  the  cylinder,  the  length  of  stroke  and  the  number  of 
explosions  or  impulses  per  minute,  and  dividing  the  product  by 
33,000. 

The  cross-sectional  area  of  the  clear  space  in  the  cylinder  is 
customarily  referred  to  as  the  piston  area.  When  there  is  no 
piston  rod  extending  through  the  combustion  space  this  area  is 
that  of  a  circle  of  the  same  diameter  as  the  bore  of  the  cylinder; 
but  when  there  is  a  piston  rod  in  the  space  its  cross-sectional 
area  must  be  deducted  from  that  of  the  circle.  The  form  of  the 
piston  head  (convex,  concave,  flat  irregular)  does  not  have  to  be 
considered. 

In  a  throttle-controlled  four-cycle  motor  of  the  common  type, 
there  is  an  explosive  impulse  every  four  strokes  of  the  piston 


2$0  THE   GAS  ENGINE 

(two  revolutions  of  the  crank)  in  each  combustion  chamber 
provided  there  are  no  misfires.  In  a  two-cycle  motor  there  is  an 
impulse  every  two  strokes  of  the  piston  (every  revolution  of  the 
crank)  under  similar  conditions. 

In  a  hit-or-miss  controlled  motor  the  number  of  explosions  per 
minute  is  variable  and  must  therefore  be  recorded  to  obtain  the 
indicated  horsepower. 

The  following  notation  will  be  used  to  write  the  mathe- 
matical expressions  for  the  indicated  horsepower  of  an  indicator 
diagram  : 

A  =  piston  area,  effective,  square  inches; 

G  =  strokes  of  piston  per  cycle; 

L  =  length  of  stroke  of  piston,  feet; 

R  =  revolutions  of  crank  per  minute; 

T  =  piston  travel,  feet  per  minute; 

Y  =  number  of  explosions  or  impulses  per  minute; 

I.h.p.I  =  impulsive    indicated     horsepower    per    combustion 

chamber; 
I.h.p.R  =  retarding    indicated     horsepower   per    combustion 

chamber; 

I.h.p.N  =  net  indicated  horsepower  per  combustion  chamber; 
M.e.p.I  =  mean  effective   impulsive  pressure  of  impulse  card 

(CDEFC,Fig.  77); 
M.e.p.R   =  mean  effective  retarding  pressure  of  pumping  card 

(ABFA,Fig.  77); 
M.e.p.N   =  M.e.p.I  —  M.e.p.R  =  net  mean  effective  pressure. 

For  the  general  case,  including  hit-or-miss  governing, 


33,000 
or 


Lh.p.N  .        ... 

33,000  G 


W  THB 

UNIVERSITY 

OF 


INDICATOR   CARDS  FROM   PRACTICE  251 

For  a  four-cycle  motor  without  misfires  or  cgmplete  cut-outs 
of  charges  (reduction  of  charge  governing), 

(M.e.p.N)  ALR 
I.h.p.N  =  -  —  •> 

2  X  33,000 

Lh.p.N 


4  X  33,000 

For  a  two-cycle  motor  without  misfires  or  complete  cut-outs  of 
charges, 

(M.e.p.N)  ALR 


Lh.p.N  = 
I.h.p.N  - 


33,000 
or 

(M.e.p.N)  AT 
2  X  33,000 


Equations  similar  to  the  above  can  be  written  for  the  mean 
effective  pressure  of  the  impulse  loop  and  for  the  pumping  loop 
of  the  diagram,  the  only  change  being  the  substitution  of  the 
proper  mean  effective  pressure  and  indicated  horsepower. 

In  a  two-Cycle  motor  the  pumping  loop  does  not  appear  on  the 
diagram.  If  the  usual  type  of  indicator,  in  which  the  pressure 
of  the  gas  acts  on  only  one  side  of  the  piston,  is  used,  it  records 
only  the  impulse  diagram.  A  separate  card  for.  the  crank  case 
of  the  simpler  type  of  two-cycle  motor  must  be  taken  for  the 
pumping  diagram.  In  the  more  complicated  forms  of  two-cycle 
motors  with  precompression  pumps,  the  pumping  diagrams  are 
to  be  taken  from  the  pumps  themselves. 

178.  Indicator  Cards  Representing  American  Practice.  —  A 
number  of  indicator  cards  from  American  gas,  gasoline,  and  oil 
motors  are  reproduced  with  as  much  accuracy  as  possible  in  this 
section.  In  some  of  them  the  bottom  loop  is  omitted  on  account 
of  its  being  so  narrow  that  it  cannot  be  read  or  reproduced  with 
a  warrantable  degree  of  accuracy.  Its  value  is  of  course  of  little 
weight  in  determining  the  indicated  power  when  the  loop  is  so 
small. 


252 


THE  GAS  ENGINE 


The  point  of  ignition  is  much  more  clearly  denned  in  Fig.  79 
than  in  Fig.  77.  The  compression  pressure  is  determined  by 
continuing  the  compression  line  as  if  there  had  been  no  ignition 


FIG.  79. 

FOUR-CYCLE  MOTOR.     HIT-OR-MISS  GOVERNED.     FULL  LOAD. 
Pressures  in  pounds  per  square  inch  above  atmosphere. 


Illuminating  gas. 

Compression  pressure 60 

Explosion  pressure 220 

M.e.p.  impulse 84 

210 
180 


150 
120 
90 


Diameter  of  piston 13 .  5* 

Stroke 24* 

Revolutions  per  minute 170 

Piston  travel,  feet  per  minute .  .  .  680 


FIG.  80. 


FOUR-CYCLE    MOTOR.     THROTTLE    GOVERNED.     PART    LOAD. 
Pressures  in  pounds  per  square  inch  above  atmosphere. 

Natural  gas.  Diameter  of  piston 15* 

Compression  pressure 63       Stroke 24* 

Explosion  pressure 200       Revolutions  per  minute 170 

M.e.p.1 58       Piston  travel,  feet  per  minute.  .  .  .    680 

till  it  intersects  the  line  perpendicular  to  the  atmospheric  line  and 
tangent  to  the  combustion  line  at  the  right-hand  end  of  the 
diagram.  The  bottom  loop  on  the  original  card  appears  almost 
as  a  line,  and  is  not  reproduced. 


INDICATOR  CARDS  FROM  PRACTICE  253 

Fig.  8 1  shows  the  effect  of  the  vibration  of  the  indicator 
point  at  the  beginning  of  the  impulse  stroke,  recorded  as  a  wavy 
line.  The  area  of  the  card  was  determined  by  drawing  a  smooth 
curve  to  represent,  as  nearly  as  could  be  judged,  the  true  pressures 
that  would  have  been  recorded  if  the  indicator  had  not  vibrated. 


100 


FIG.  81. 
FOUR-CYCLE  MOTOR.     HIT-OR-MISS  GOVERNED.     FULL  LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Illuminating  gas .  Diameter  of  piston i  r .  25* 

Compression  pressure 72       Stroke 19" 

Explosion  pressure ' 334       Revolutions  per  minute 220 

M.e.p.1 96. 5  Piston  travel,  feet  per  minute.  .  .      697 

In  this  motor  the  ignition  is  electric  in  a  small  chamber  con- 
nected to  the  combustion  chamber  by  a  straight  narrow  passage 
so  that  a  flame  spurts  out  into  the  main  body  of  the  charge  to 
ignite  it. 

In  Fig.  82  the  sharp  peak  at  the  top  of  the  diagram  with 
rapidly  rising  combustion  line  at  the  peak  seems  to  indicate  that 
a  sharp  local  explosion  occurred  in  the  connections  to  the  indicator 
after  the  combustion  of  the  main  body  of  the  charge  was  well 
under  way. 

The  bottom  loop  of  this  card  shows  that  the  exhaust  pressure 
dropped  to  about  atmospheric  when  the  piston  was  about  one- 
quarter  of  the  way  back  on  the  exhaust  stroke  and  then  rose 
higher  later  in  the  stroke.  This  might  be  caused  by  a  very  quick 
and  full  opening  of  the  exhaust  valve  together  with  a  straight 
exhaust  pipe  of  such  proportions  that  the  inertia  of  the  escaping 


254 


THE  GAS  ENGINE 


gas  tended  to  form  a  partial  vacuum  soon  after  their  release, 
which  tendency  did  not  continue  till  the  middle  of  the  stroke  was 
reached. 

— 1 420 


240 
ISO 
120 


FIG.  82. 

FOUR-CYCLE  MOTOR.     HIT-OR-MISS  GOVERNED.     FULL  LOAD. 
Pressures  in  pounds  per  square  inch  above  atmosphere. 

Natural  gas.  Diameter  of  piston 15 1* 

Compression  pressure 100       Stroke 18* 

Explosion  pressure 375       Revolutions  per  minute 175 

M.e.p.1 104      Piston  travel,  feet  per  minute  ....    525 


FIG.  83. 

FOUR-CYCLE  MOTOR.     THROTTLE  GOVERNED.     FULL  LOAD. 
Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gas.  Diameter  of  piston 19* 

Compression  pressure 92       Stroke 24" 

Explosion  pressure 270       Revolutions  per  minute 225 

M.e.p.1 71.2       Piston  travel,  feet  per  minute 900 

See  Fig.  84  for  card  from  same  motor  throttled  to  about  seven  per  cent  of  the  full 

load  at  the  brake. 

The  lower  loop  of  Fig.  83  has  a  larger  area  on  account  of 
the  comparatively  high  piston  speed  than  it  would  "have  at  the 
lower  piston  speeds  of  the  preceding  cards. 


INDICATOR   CARDS  FROM  PRACTICE  255 

Fig.  84  shows  two  consecutive  diagrams  dntwn  by  keeping 
the  tracing  point  on  the  card  during  two  cycles  of  the  motor. 

Both  combustion  lines  slope  away  from  the  perpendicular  to 
the  atmospheric  line.  This  is  due  to  the  slower  rate  of  inflamma- 
tion and  combustion  on  account  of  both  the  lower  degree  of  com- 
pression and  the  greater  dilution  of  the  mixture  than  in  Fig.  83. 
The  time  of  ignition  is  the  same  for  all  three  of  the  diagrams 


FIG.  84. 

FOUR-CYCLE  MOTOR.  THROTTLE  GOVERNED.  THROTTLED 
TO  ABOUT  SEVEN  PER  CENT  OF  THE  FULL  CAPACITY  BRAKE 
LOAD  AS  DELIVERED  BY  THE  MOTOR. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gas.  Diameter  of  piston ig" 

Compression  pressure 32       Stroke 24" 

_     .     .  (58       Revolutions  per  minute 232 

Explosion  pressure <  ~.         _. 

(  64       Piston  travel,  feet  per  minute  ....     928 

M.e.p.L,  average 14.6 

See  Fig.  83  for  full-load  card  from  same  motor. 

shown  in  the  two  cards.  It  occurs  a  little  before  the  completion 
of  the  compression  stroke  in  each  case.  The  slower  rate  of  com- 
bustion and  the  lower  explosion  pressure  in  the  smaller  of  the  two 
diagrams  in  Fig.  84  is  probably  due  to  less  fuel  in  the  charge 
for  the  smaller  card,  for  the  compression  pressure  is  the  same  in 
both,  as  near  as  can  be  determined  from  a  comparatively  clear 
original  card. 

The  slope  of  the  combustion  line  away  from  the  perpendicular 
to  the  atmospheric  line  would  be  greater  if  the  indicator  spring 
were  of  the  same  strength  as  that  used  for  Fig.  83  instead  of 
being  80  pounds  per  inch  of  compression  while  that  of  Fig.  83  is 
200  pounds  per  inch  of  compression. 


256 


THE   GAS  ENGINE 


The  expansionline  of  the  light-load  card  drops  to  within  a  pound 
or  two  of  atmospheric  pressure.  In  the  full-load  card  its  lowest 
point  is  about  twenty  pounds  above  atmosphere. 

The  suction  line  of  the  light-load  card  falls  to  about  six  pounds 
below  atmosphere  soon  after  the  beginning  of  the  charging  stroke, 
and  continues  to  fall  gradually  to  about  eight  pounds  below  atmos- 
phere at  the  completion  of  the  charging  stroke.  The  area  of 
the  lower  loop  is  not  great,  however,  since  the  compression  line 
follows  it  closely  back  about  half  way. 

The  suction  line  in  Fig.  84  rises  above  the  exhaust  line  during 
the  early  part  of  the  charging  stroke.  This  is  probably  due  to  a 
momentary  increase  of  back  pressure  in  the  exhaust  pipe,  caused 
by  the  exhaust  from  another  combustion  chamber  of  the  motor  at 
about  the  time  of  the  completion  of  the  exhaust  stroke  of  this  card 
and  while  the  corresponding  exhaust  valve  was  closed.  It  may 
be  due  to  slight  lost  motion  in  the  indicator,  but  this  is  hardly 
probable,  since  the  cards  come  from  one  of  the  leading  gas-engine 
builders. 


FIG. 

FOUR-CYCLE  MOTOR.     THROTTLE  GOVERNED.     FULL  LOAD. 
Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gas .  Diameter  of  piston 8" 

Compress  on  pressure 80       Stroke lo* 

Explosion  pressure 380       Revolutions  per  minute. 320 

M.e.p.1 82       Piston  travel,  feet  per  minute 533 

See  Fig.  86  for  light- load  card  from  same  motor. 


INDICATOR  CARDS  FROM  PRACTICE  257 

The  extreme  sharpness  and  height  of  the  peak  in  Fig.  85  are 
probably  due  to  the  inertia  of  the  moving  parts  of  the  indicator 
causing  it  to  record  higher  than  the  actual  maximum  pressure 
of  the  explosion.  The  sharp  waves  of  the  expansion  line  are 
records  of  rapid  vibration  of  the  indicator  tracing  point  on  account 
of  the  inertia  of  the  parts. 


FIG.  86. 


FOUR-CYCLE    MOTOR.      THROTTLE     GOVERNED.      THROTTLED 
TO   RUN   ON   ITS   OWN   FRICTION   LOAD   ONLY. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gas.  Diameter  of  piston 8" 

Compression  pressure 22  Stroke 10" 

Explosion  pressure 37  Revolutions  per  minute 331 

M.e.p.1 12.4  Piston  travel,  feet  per  minute  ....  550 

See  Fig.  85  for  full-load  card  from  same  motor. 

Fig.  86  represents  an  extreme  case  of  the  retarding  effects  of  low 
compression  and  great  dilution  on  the  rate  of  flame  propagation 
and  combustion.  The  card  was  taken  from  the  same  motor  as 
that  of  Fig.  85.  The  time  of  ignition  was  the  same  in  both  cases 
slightly  before  the  completion  of  the  compression  stroke. 

The  linear  rate  of  flame  propagation  is  so  slow  in  Fig.  86  that 
the  pressure  of  combustion  is  scarcely  kept  up  to  that  of  compres- 
sion during  the  early  part  of  the  impulse  stroke.  But  the  rapidly 
increasing  volume  rate  of  propagation  then  causes  the  pressure  to 
rise  notwithstanding  the  increase  in  the  rate  of  the  travel  of  the 
piston  and  in  the  rate  of  increase  of  volume  of  the  enclosed  gases.* 

*  The  propagating  flame  moves  out  from  the  point  of  ignition  with  the  same 
constant  linear  velocity  in  all  directions  (theoretically  in  a  quiescent  body  of 
gas).  The  crest  of  the  propagating  flame  therefore  forms  a  spherical  surface 
whose  area  increases  as  the  square  of  the  diameter  or  of  the  time  elapsed  after 
the  initial  ignition.  The  rate  of  inflammation,  measured  in  the  volume  inflamed 
per  unit  time,  therefore,  increases  as  the  square  of  the  time.  And  the  total 


258  THE  GAS  ENGINE 

The  short  horizontal  portion  of  the  combustion  line  may  be  in 
part  due  to  friction  in  the  indicator  after  coming  to  rest  at  the 
completion  of  compression.  In  such  a  case  it  would  at  first  move 
more  rapidly  immediately  after  starting  from  rest  than  the  in- 
creasing pressure  of  the  gases  alone  would  cause.  Such  an  action 
will  produce  a  sharp  bend  in  the  curve  such  as  that  between  the 
short  horizontal  line  and  the  upward  inclined  line. 

If  the  load  on  the  motor  is  increased  by  successive  steps  from 
only  the  friction  load,  Fig.  86,  to  full  load,  Fig.  85,  the  inclination 
of  the  combustion  line  from  the  vertical  on  cards  taken  for  each 
step  of  increase  of  load,  will  decrease  as  the  load  increases,  finally 
reaching  the  direction  of  that  in  Fig.  85  for  full  load. 

The  same  is  true  of  Figs.  83  and  84. 

The  maximum  pressures  in  Figs.  83  and  84  for  full  load  and 
light  load  occur  at  about  the  same  time  in  the  stroke.  But  in 
Fig.  86  the  maximum  pressure  is  much  later  than  for  the  full- 
load  card,  Fig.  85,  from  the  same  motor. 

Two  diagrams  taken  consecutively  from  a  hit-or-miss  governed 
motor  with  friction  load  only  are  shown  in  Fig.  87.  One 
diagram  was  made  after  a  charge  was  cut  out  by  the  governor 
action,  and  the  other  for  the  following  impulse  stroke.  The 
compression  lines  of  the  two  diagrams  are  coincident  except  for 
a  short  distance  just  before  the  completion  of  compression.  They 
then  separate  slightly  and  the  distance  between  them  continues 
to  increase  till  the  end  of  the  compression  stroke. 

The  impulse  line  of  the  full-charge  diagram  lies  above  the 
compression  line  in  the  usual  manner.  The  expansion  line  of 
the  cut-out  diagram  drops  slightly  below  the  compression  line 
during  the  stroke  following  compression  (normally  the  impulse 
stroke).  The  drop  of  this  expansion  line  at  and  near  the  end 
of  the  compression  stroke  is  probably  chiefly  due  to  leakage.  The 
" exhaust"  line  following  expansion  of  the  cut-out  charge  cannot 

volume  of  the  gas  inflamed  increases  as  the  volume  of  the  sphere,  or  as  the 
cube  of  the  time,  the  linear  rate  of  propagation  remaining  constant.  Some 
approximation  of  this  condition  probably  occurs  in  a  motor  when  the  ignition 
is  at  a  point  in  the  main  body  of  the  charge,  as  distinguished  from  ignition  in 
a  pocket  leading  off  from  the  mass  of  the  gas. 


INDICATOR  CARDS  FROM  PRACTICE 


259 


FIG.  87. 

FOUR-CYCLE  MOTOR.     HIT-OR-MISS  GOVERNED.     FRICTION 

LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Natural  gas  Diameter  of  piston 13* 

Compression  pressure 70       Stroke 22" 

Explosion  pressure 310       Revolutions  per  minute 170 

M.e.p.1 90       Piston  travel,  feet  per  minute  ....  623 


FIG.  88. 


FIG.  89. 


260 


THE  GAS  ENGINE 


be  distinguished  from  the  suction  line,  but  probably  lies  very 
slightly  above  it. 

Fig.  88  shows  a  series  of  indicator  cards  from  a  gas  motor 
governed  by  a  cut-off  valve  that  allows  the  mixture  to  begin  to 
enter  at  the  beginning  of  the  suction  stroke  and  cuts  it  off  during 
the  suction  stroke  when  a  volume  proportional  approximately 
to  the  work  being  done  by  the  motor  has  entered  the  cylinder. 

Fig.  89  shows  the  corresponding  diagrams  taken  with  a  low 
spring  and  stop  on  the  indicator. 


FIG.  90. 


FIG.  91. 

Figs.  90  and  91  are  cards  from  the  "  complete  expansion 
engine."  They  show  respectively  the  upper  loops  of  a  pair  of 
diagrams  and  the  corresponding  low-spring  cards.  The  motor 
is  four  cycle  and  governed  by  admitting  only  air  during  the 
first  part  of  the  suction  stroke,  and  then  beginning  the  admission 


INDICATOR  CARDS  FROM  PRACTICE 


26i 


of  gas  at  a  time  determined  by  the  governor.  '  The  gas  and 
air  are  both  cut  off  at  the  same  instant  at  about  half  stroke. 


FIG.  92. 

Fig.  92  is  a  series  of  diagrams  from  the  same  kind  of  a 
motor  as  that  from  which  Figs.  90  and  91  were  obtained.  It 
shows  the  governing  action  during  fifty  consecutive  cycles. 


192 
160 


FIG.  93. 

FOUR-CYCLE  MOTOR.     HIT-OR-MISS  GOVERNED.     FULL  LOAD. 
Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gasoline .  Diameter  of  piston r  2" 

Compression  pressure 50       Stroke 2o" 

Explosion  pressure 245       Revolutions  per  minute 2oo 

M.e.p.1 82       Piston  travel,  feet  per  minute.  . .  .  667 

Three  consecutive  diagrams  from  a  hit-or-miss  governed  motor 
are  shown  in  Fig.  93.  The  ignition  was  at  the  same  time  in 
each.  The  rate  of  combustion  (or  of  flame  propagation)  is  dif- 
ferent in  each,  however,  as  shown  by  the  different  inclinations  of 
the  combustion  lines.  The  areas  and  mean  effective  pressures 
are  practically  the  same  in  all  three.  This  indicates  that  the 


262 


THE  GAS  ENGINE 


same  weight  of  fuel  was  burned  and  the  same  amount  of  heat 
energy  produced  by  the  combustion  of  each  charge.  All  the 
charges  were  drawn  in  under  the  same  condition  of  inlet  passages, 
carbureter,  and  other  parts,  by  virtue  of  the  method  of  governing. 
The  coincidence  of  the  compression  lines  also  shows  that  the 
charges  were  of  the  same  weight. 

The  difference  in  the  rate  of  inflammation,  or  of  combustion, 
or  of  both,  was  probably  due  to  a  difference  in  the  thoroughness 
of  the  mixture  of  the  fuel  and  the  air,  or  of  its  richness  at  and  in 
the  neighborhood  of  the  ignition  apparatus. 


200 

160 

120 

80 

40 


FIG.  94. 

FOUR-CYCLE  MOTOR.     HIT-OR-MISS  GOVERNED.     LIGHT  LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gasoline.                                                           Diameter  of  piston 12* 

Stroke 20* 

Revolutions  per  minute 200 

Piston  travel,  feet  per  minute  ....  667 


Compression  pressure 

Explosion  pressure 

M.e.p.I 


60 

270 
330 


94 


Fig.  94  shows  three  diagrams  from  the  same  motor  as  that 
from  which  the  preceding  set  of  cards,  Fig.  93,  was  taken,  but 
the  motor  was  running  on  light  load  in  the  last  card.  The  large 
diagram  is  for  the  first  explosion  after  several  misfires.  This 
was  followed  immediately  by  the  smaller  implilse  diagram. 
The  cut-out  diagram  is  a  composite  of  several  diagrams. 


INDICATOR  CARDS  FROM  PRACTICE 


263 


The  greater  size  of  the  larger  diagram  is  due  either  to  a  greater 
weight  of  fuel  or  a  better  proportion  of  the  mixture.  A  greater 
weight  of  mixture  is  generally  drawn  into  the  cylinder  after 
several  cut-outs  on  account  of  the  cylinder  becoming  cooler.  An 
inlet  valve  that  lets  combustible  mixture  leak  into  the  cylinder 
during  the  suction  stroke  when  the  charge  is  cut  out  (as  on 
account  of  too  weak  a  valve  spring)  will  allow  scavenging  of 
the  cylinder  during  several  consecutive  cut-out  strokes,  so  that  the 
following  charge  is  but  slightly  diluted  by  the  inert  products  of 
combustion.  The  resulting  diagram  is  then  larger  than  those 
following. 

The  cut-out  diagram  in  this  card  shows  but  little,  if  any,  leakage. 
The  expansion  line  of  the  cut-out  diagram  will  fall  below  the 
compression  line  when  the  cylinder  is  cool,  even  if  there  is  no 
leakage  from  the  cylinder,  for  some  of  the  heat  of  compression 
is  given  up  to  the  cylinder  during  the  time  the  gas  is  well  com- 
pressed. The  same  may  also  be  true  with  a  hot  cylinder  when 
the  incoming  charge  strikes  the  hottest  parts,  as  the  exhaust 
valve  and  ports,  and  the  piston  head  when  not  water  cooled.  In 
such  a  case  the  charge  becomes  so  highly  heated  while  entering 
that  its  compression  temperature  is  higher  than  that  of  the  cylinder 
walls  taken  as  an  average. 


210 
180 
150 
120 
90 


FIG.  95. 
FOUR-CYCLE    MOTOR.     THROTTLE    GOVERNED.     FULL    LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gasoline.                                                           Diameter  of  piston 10.5* 

Compression  pressure 60       Stroke 14" 

Explosion  pressure 210       Revolutions  per  minute 250 

M.e.p.1 76       Piston  travel,  feet  per  minute 583 


264  THE  GAS  ENGINE 

Fig.  95  shows  a  card  with  two  diagrams  from  a  gasoline 
motor  of  the  throttle-governed  type.  There  is  considerable 
difference  in  the  combustion  lines,  although  the  compression  lines 
coincide  so  far  as  can  be  seen  on  the  original,  clearly  drawn,  fine 
line  card.  The  higher  combustion  line  has  a  decided  reverse 
curve,  which  seems  to  indicate,  as  in  Fig.  82,  that  there  was  a 
sharp  explosion  in  the  connections  between  the  indicator  and  the 
combustion  chamber  after  the  main  body  of  the  gas  was  well 
inflamed.  The  expansion  line  of  the  higher  card  with  the  peaked 
top  falls  below  that  of  the  other,  so  that  the  areas  of  the  two  cards 
are  practically  equal. 


FIG.  96. 

FOUR-CYCLE  MOTOR.     HIT-OR-MISS  GOVERNED.     FULL  LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Gasoline.                                                           Diameter  of  piston 6. 75* 

Compression  pressure 62       Stroke 15. 5* 

Explosion  pressure 360       Revolutions  per  minute 260 

M.e.p.1 102       Piston  travel,  feet  per  minute. . .  672 

Motor  took  126  charges  per  minute. 

In  Fig.  96  the  sharp  angle  between  the  compression  line 
and  the  combustion  line  indicates  ignition  at  the  completion  of 
the  compression  stroke.  It  compares  in  this  case  with  Fig.  81 
from  a  motor  of  the  same  make  operating  on  illuminating  gas. 

In  both  motors,  Figs.  81  and  96,  the  ignition  plug  is 
placed  in  a  small  chamber  connected  to  the  combustion  chamber 
by  a  small  passage.  The  spark  ignites  the  gas  in  the  small 


INDICATOR  CARDS  FROM  PRACTICE  265 

chamber  and  the  expansion  of  the  gas  while  burning  projects  a 
flame  into  the  body  of  the  charge  in  the  combustion  chamber, 
thus  inflaming  a  considerable  amount  of  the  charge  suddenly. 
The  gas  currents  caused  by  the  projection  of  the  gas  and  flame 
from  the  ignition  pocket  into  the  combustion  chamber  also  help 
the  rapidity  of  inflammation.  This  method  of  ignition  accounts 
for  the  absence  of  the  rapid  falling  away  of  the  combustion  line 
from  the  vertical,  which  occurs  when  ignition  is  at  the  completion 
of  the  compression  stroke  by  a  spark  or  arc  in  the  main  body  of 
the  gas  in  the  combustion  chamber. 


200 

100 
120 


40 
0 

FIG.  97. 

FOUR-CYCLE  MOTOR.     GOVERNED  BY  REGULATING  THE 
AMOUNT  OF  FUEL  PER  CHARGE.     FULL  LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 

Kerosene.  Diameter  of  piston 6.5* 

Compression  pressure 40       Stroke g" 

(  1150       Revolutions  per  minute 405 

Explosion  pressure <  ^.  .   , 

(  170       Piston  travel,  feet  per  minute 607 

M.e.p.1 63 

In  Fig.  97  ignition  occurs  rather  late,  at  dead  center  or  very 
slightly  before  it,  as  indicated  by  the  nearly  horizontal  direction 
of  the  first  part  of  the  combustion  line.  The  difference  of  the 
areas  of  the  two  cards  is  due  to  the  varying  quantity  of  combustible 
mixture. 

In  Fig.  98  the  three  diagrams  are  from  a  Hornsby-Akroyd 
motor  operating  at  full  load.  The  difference  in  the  areas  of  the 
diagrams  is  due  to  the  governor  action  in  regulating  the  amount 
of  liquid  fuel  that  is  injected  into  the  vaporizer  extension  of  the 
motor  cylinder  during  each  cycle.  The  compression  is  of  course 


266 


THE   GAS  ENGINE 


always  practically  the  same,  since  air  is  always  freely  admitted 
during  the  suction  stroke.  Ignition  occurs  some  time  before  the 
completion  of  the  compression  stroke,  and  is  caused  by  the  high 
temperature  of  the  walls  of  the  vaporizer. 


200 

180 

160 

140 

120 

100 

80 

60 

40 

20 

0 


FIG.  98. 


HORNSBY-AKROYD  FOUR-CYCLE  MOTOR.  GOVERNED  BY  REGU- 
LATING THE  AMOUNT  OF  FUEL  PER  CHARGE.  FULL  LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 


Distillate  of  petroleum. 

Compression  pressure 

Explosion  pressure,  average.. 
M.e.p.I.  average 


Diameter  of  piston 23* 

58       Stroke 28* 

180       Revolutions  per  minute 160 

54       Piston  travel,  feet  per  minute 747 


With  regard  to  Fig.  99  it  will  be  remembered  that  the  full 
charge  of  air  is  taken  in  and  compressed  to  a  high  pressure  before 
the  liquid  fuel  is  injected  (blown)  into  the  combustion  chamber, 
and  that  ignition  is  caused  by  the  heat  of  compression.  The 
work  of  compressing  the  air  to  blow  the  fuel  into  the  combustion 
chamber  must  be  deducted  from  that  of  the  impulse  card  to 
determine  the  net  indicated  power. 

Fig.  100  is  a  low-spring  or  pumping  card  corresponding  to 
Fig.  99. 

Fig.  101  is  a  card  from  a  Koerting  two-cycle  motor,  which 
has  auxiliary  cylinders  for  separately  compressing  the  air  and  gas. 


FIG.  99. 

DIESEL  TWO-CYCLE  MOTOR.  GOVERNED  BY  REGULATING  THE 
AMOUNT  OF  FUEL  PER  CHARGE.  FULL  LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 


Petroleum  distillate,  specific  gravity.   .85 

Compression  pressure 480 

Combustion  pressure 490 

M.e.p.1 97 


Diameter  of  piston 16" 

Stroke. 24" 

Revolutions  per  minute 160 

Piston  travel,  feet  per  minute 640 


Suction 

FIG.  100. 


204 
170 


102 


34 


FIG.  101. 

KOERTING  TWO-CYCLE  MOTOR.     GOVERNED  BY  REGULATING 
THE  AMOUNT   OF   FUEL   PER   CYCLE.     FULL  LOAD. 

Pressures  in  pounds  per  square  inch  above  atmosphere. 
Producer  gas.  Diameter  of  piston 25  •  5* 


Compression  pressure 120 

Explosion  pressure 225 

M.e.p.I 53 


Stroke 45 

Revolutions  per  minute 100 

Piston  travel,  feet  per  minute 750 


268  THE  GAS  ENGINE 

The  governing  is  by  admitting  the  gas  during  the  latter  part  of 
the  charging  stroke  for  such  a  length  of  time  as  the  governor 
determines. 

The  exhaust  comes  earlier  than  in  a  properly  adjusted  four- 
cycle motor  on  account  of  the  necessity  of  having  the  piston 
uncover  the  exhaust  port  early  enough  to  allow  the  spent  gases 
to  escape  and  the  new  charge  to  enter  while  the  port  remains 
uncovered. 

The  pumping  or  charging  diagram  does  not  appear  on  the  card, 
since  this  part  of  the  work  is  done  in  the  two  auxiliary  cylinders. 
Separate  diagrams  must  be  taken  from  the  auxiliary  cylinders  to 
obtain  the  pumping,  or  charging,  diagrams. 

179.  Indicator    Diagrams    Showing    Abnormal    Pressures.  — 
If  the  pipe  connections  to  the  indicator  are  long,  and  especially 
if  the  passage  is  contracted  at  the  end  next  the  combustion 
chamber,  the  combustion  of  the  gas  hi  the  pipe  after  the  pressure 
has  become  high  in  the  combustion  chamber  on  account  of  the 
explosion,    will    generally   give   diagrams    showing    abnormally 
high   and   suddenly   increasing  pressures.     The   inertia  of  the 
moving  parts  of  the  indicator  adds  to  the  recorded  apparent 
pressure.     Pockets  in  the  combustion  space  of  the  motor  will 
give  similar  but  generally  less  marked  results  when  the  ignition 
is  not  in  the  pocket. 

It  has  already  been  pointed  out  that  the  indicator  connections 
should  be  as  short  as  possible,  and  without  contracted  passages. 

180.  Incorrect  Valve  Setting  as  Shown  by  the  Indicator  Diagram. 
Four-Cycle  Motors.  —  Figs.  102  to  107  are  portions  of  indicator 
diagrams  showing  the  characteristic  effects  of  extremely  early  or 
late  opening  or  closing  of  the  inlet  and  exhaust  valves.     Those 
for  the  inlet  valve  apply  only  to  those  that  are  mechanically 
operated  valves. 

Fig.  1 02  shows  the  latter  part  of  the  expansion  line  and  the 
early  part  of  the  exhaust  line.  The  early  opening  of  the  exhaust 
allows  the  burned  gases  to  escape  before  the  expansive  action  and 
impulse  pressure  against  the  piston  are  completed  as  far  as  is 
practicable  and  advantageous  and  can  be  done  without  causing 
too  much  pressure  against  the  piston  during  the  early  part  of 


INDICATOR  CARDS  FROM  PRACTICE  269 

the  exhaust  stroke.     The  result  is  a  reduction  of.  the  area  of  the 
impulse  loop  and  of  the  mean  effective  pressure  of  the  impulse. 


Exhaust 


FIG.  102. 

This  should  not  be  confused  with  the  necessary  earlier  exhaust 
of  the  two-cycle  motor,  as  compared  with  the  four-cycle  type. 

Fig.  103  indicates  too  late  an  opening  of  the  exhaust  valve. 
This  causes  considerable  pressure  resisting  the  motion  of  the 


Exhaust 


FIG.  103. 

piston  during  the  early  part  of  the  exhaust  stroke.    The  area  of  the 
impulse  loop  and  the  mean  effective  pressure  are  both  reduced. 

Fig.  104  is  characteristic  of  an  exhaust  valve  closing  too  early 
when  the  inlet  valve  opens  at  the  end  of  the  stroke.  When 
the  inlet  valve  opens  under  this  condition,  the  slightly  compressed 

Vs     • Exhaust         •< 


Suction 

FIG.  104. 


exhaust  gases  puff  out  into  the  inlet  passage  and  are  then  drawn 
in  again  as  the  piston  moves  out  on  the  suction  stroke.  This 
causes  fouling  of  the  inlet  valve  and  its  stem,  and  is  a  condition 
that  should  be  particularly  avoided. 


270  THE  GAS  ENGINE 

In  Fig.  105  the  exhaust  valve  closes  too  early,  as  in  the 
preceding  figure,  but  the  inlet  valve  opens  later  than  it  should 
for  proper  setting  of  the  exhaust  valve.  The  conditions  of 
Fig.  105  are  better  than  those  of  Fig.  104  mainly  because  there  is 


Exhaust 


Suction          >• 

FIG.  106. 

no  puffing  out  of  the  exhaust  gases  through  the  inlet  valve,  but 
also  because  the  area  of  the  pumping  card  loop  is  smaller.  The 
latter  is  generally  insignificant  in  comparison  with  the  former. 

Fig.  106  indicates,  by  the  horizontal  portion  of  the  com- 
pression line,  too  late  closing  of  the  inlet  valve.  Under  this 
condition  part  of  the  charge  that  has  been  drawn  in  and  diluted 


by  the  residual  inert  gases  is  forced  back  through  the  inlet  valve 
during  the  early  part  of  the  compression  stroke.  Compression 
does  not  begin  till  the  inlet  valve  closes.  The  following  charge 
is  somewhat  weakened,  or  made  lean,  by  the  inert  gases  that  were 
forced  back  into  the  inlet  passage,  and  the  power  of  the  motor 
is  thus  reduced. 

Fig.  107  shows  early  closing  of  the  inlet  valve.  This  is 
accompanied  with  no  undesirable  results.  The  charge  is  rarefied 
after  the  inlet  valve  closes,  and  then  compressed  along  the  same 
line  again  up  to  suction  pressure,  after  which  the  compression 
continues  in  the  usual  manner.  This  is  characteristic  of  the 
method  of  governing  by  reducing  the  amount  of  the  mixture  per 


INDICATOR  CARDS  FROM  PRACTICE  271 

charge  by  opening  the  mixture  inlet  valve  always  at  the  same 
time  and  closing  it  at  such  a  part  of  the  stroke  as  the  speed  and 
governor  determine. 


FIG.  107. 

This  method  of  operation  is  also  characteristic  of  the  "  complete 
expansion  "  engine. 

181.  Momentary  Back  Pressure.  —  Fig.  108  shows  the  effect 
of  back  pressure  in  the  exhaust  pipes  at  the  time  of  exhaust 
of  another  cylinder  whose  exhaust  opens  one-half  a  revolution 
from  that  of  the  cylinder  from  which  the  indicator  card  is  taken. 


Exhaust 


Suction          >• 

FIG.  108. 

The  back  pressure  comes  into  the  cylinder  just  before  the  exhaust 
valve  closes,  and  drops  when  the  inlet  valve  opens  (after  the 
exhaust  valve  has  closed).  This  is  not  an  indication  of  incorrect 
valve  setting.  (See  disposal  of  exhaust  gases.) 

182.  Variation  of  the  Time  of  Ignition  as  Affecting  the  Indi- 
cator Card.  Four-Cycle  Motor. — When  all  the  other  conditions 
remain  constant,  and  the  time  of  ignition  is  varied,  the  effects  on 
the  indicator  diagram  are  shown  characteristically  in  Figs.  109 
to  in. 


2/2 


THE  GAS  ENGINE 


Fig.  109  indicates  ignition  that  is  later  than  is  suitable  for 
the  best  results  in  economy  of  fuel  in  motors  of  the  usual  con- 
struction. The  great  inclination  of  the  combustion  line  is  due  to 


FIG.  109. 

the  rapid  increase  of  volume  of  the  burning  gases  as  the  piston 
travels  out,  and  also  to  the  consequent  lower  rate  of  flame  propa- 
gation and  combustion  on  account  of  the  rarefication  of  the  charge 
by  the  movement  of  the  piston. 

In  Fig.  no  the  ignition  is  extremely  late,  not  occurring  till 
the  piston  has  moved  out  some  distance  on  the  impulse  stroke. 
The  completion  of  compression  and  the  early  part  of  the  impulse 


FIG.  110. 

stroke  are  therefore  the  same  as  for  a  cut-out  stroke  of  a  hit-or- 
miss  governed  motor.  The  combustion  line  rises  very  slowly 
on  account  of  the  comparative  low  pressure  of  the  charge  at  the 
time  of  ignition  and  the  consequent  slower  rate  of  flame  propa- 
gation; also  on  account  of  the  speed  of  piston  travel  being 
greater  after  the  piston  has  moved  out  some  distance  on  the  im- 
pulse stroke  than  it  is  near  the  beginning  of  the  stroke. 

Fig.  in  indicates  extremely  early  ignition.  The  explosion 
pressure  rises  to  its  maximum  before  the  completion  of  the  com- 
pression stroke,  and  then  drops  before  the  piston  has  moved  far 
out  on  the  impulse  stroke,  thus  causing  a  loop  at  the  top  of  the 


INDICATOR  CARDS  FROM  PRACTICE 


273 


card.  The  area  of  this  loop  indicates  retarding  action  on  the 
motion  of  the  piston.  The  pressure  falls  so  as  to  make  a  low 
expansion  line. 

The  area  of  the  impulse  card  is  the  difference  of  the  areas  of 
the  two  upper  loops  in  a  complete  card.     This  condition  could 


FIG.  111. 

hardly  exist  for  any  considerable  length  of  time  in  a  single- 
cylinder,  single-acting  motor,  on  account  of  the  small  amount  of 
power  that  the  motor  would  deliver.  But  it  can  occur  con- 
tinuously in  one  cylinder  of  a  multi-cylinder  motor,  as  on  account 
of  a  defect  in  the  timer  affecting  that  cylinder  only,  and  the  motor 
will  continue  to  run  by  the  impulses  of  the  other  cylinders. 


FIG.  112. 


183.  A  dilute  mixture  gives  the  full-line  part  diagram  of 
Fig.  112  in  comparison  with  the  broken -line  part  diagram  for 
a  normal  mixture  in  the  same  figure.  The  greater  inclination 
of  the  combustion  line  and  the  lower  maximum  pressure  for  the 


274 


THE  GAS  ENGINE 


dilute  mixture  are  both  due  to  the  slower  rate  of  combustion  and 
the  smaller  amount  of  total  heat  liberated  by  combustion  of  the 
charge. 

184.   Variation  of  Compression  Effects  on  the  Indicator  Dia- 
gram.—  Fig.  113  shows  two  diagrams  such  as   come  from  a 


FIG.  113. 

motor  when  its  compression  is  changed  while  all  the  other  con- 
ditions remain  the  same,  including  the  weight  and  heat  value  of 
the  charge. 

185.  Speed.  Variation  Effects  on  the  Indicator  Diagram.  - 
Changing  the  speed  of  the  motor  while  all  the  other  conditions 
remain  constant  has  an  effect  on  the  diagram  that  is  of  the  same 
nature  as  diluting  the  mixture.  It  may  be  remembered  that 
increasing  the  speed  of  rotation  of  a  motor  causes  the  ignition  to 
become  later  for  any  form  of  electric  ignition  apparatus  other 
than  the  interrupted-current  type  with  contact  points  separated 
by  the  action  of  rigid  mechanism.  The  writer's  experience  with 
a  four-cylinder  motor  having  the  latter  type  of  ignition  system, 
operating  at  too  high  a  speed  to  take  indicator  cards,  has  been 
that  the  motor  gives  practically  its  maximum  torque  at  high 
and  low  speeds  without  changing  the  time  of  ignition  when  the 
speed  varied  from  300  to  more  than  1000  revolutions  per  minute. 
The  speed  of  rotation  of  the  electric  generator  was  proportional 
to  that  of  the  motor.  A  stronger  or  "hotter"  arc  was  therefore 
drawn  at  the  igniter  at  high  speed  than  at  low.  This  naturally 
tended  to  decrease  the  time  interval  between  the  separation  of 
the  contact  points  and  the  complete  inflammation  of  the  charge, 


INDICATOR  CARDS  FROM  PRACTICE  275 

and  thus  to  counteract,  in  a  measure  at  least,  the  effect  of  the 
increased  speed  in  modifying  the  form  of  the  indicator  diagram. 

But  when  the  jump-spark  ignition  system  with  an  induction 
coil  and  vibrating  interrupter  was  put  into  action  and  the  other 
thrown  out,  a  very  considerable  advance  of  the  timer  was  necessary 
to  obtain  the  maximum  torque  at  high  speed  when  the  motor  was 
speeded  up. 

Therefore,  could  indicator  diagrams  have  been  taken  in  this 
latter  case,  there  would  undoubtedly  have  been  a  greatly  inclined 
combustion  line  and  low  explosion  pressure  when  the  speed  was 
increased  and  before  the  timer  was  advanced. 


CHAPTER  XV. 
ECONOMY  AND  EFFICIENCY. 

1 86.   Units  of  Heat  Energy  and  Mechanical  Energy.  —  The 

function  of  the  internal-combustion  motor  is  to  transform  the 
heat  energy  of  the  fueHnto  mechanical  energy  which  is  delivered 
to  machinery  or  other  apparatus  that  is  driven  by  the  power 
developed  by  the  motor. 

In  order  to  deal  with  the  economy  and  efficiency  of  the  trans- 
formation, it  is  necessary  to  select  units  for  measuring  the  heat 
energy  and  the  mechanical  energy. 

The  foot-pound  (ft.-lb.)  is  the  unit  of  measure  of  mechanical 
energy  most  used  in  this  country.  It  is  the  energy  required  to 
lift  one  pound  (avoirdupois)  one  foot  high.  (Strictly  at  about 
sea  level.  A  mass  that  weighs  one  pound  on  spring  scales  at 
sea  level  weighs  less  at  higher  altitudes.) 

The  horsepower  (h.p.)  is  the  unit  of  the  rate  of  working  or  of 
delivering  mechanical  energy.  The  mechanical  value  of  a 
horsepower  is  550  foot-pounds  per  second  =  33,000  foot-pounds 
per  minute  =  1,980,000  foot-pounds  per  hour. 

The  British  thermal  unit  (B.t.u.)  is  the  measure  of  heat  energy 
most  used  in  this  country.  It  is  the  amount  of  heat  that  will 
raise  the  temperature  of  one  pound  (avoirdupois)  of  water  one 
degree  by  the  Fahrenheit  thermometer  scale,  starting  from  the 
temperature  of  maximum  density  of  the  water  (39.1°  F.  about). 

The  heat  value  of  a  fuel  is  stated,  in  the  discussion  which 
follows,  in  the  number  of  British  thermal  units  that  a  specified 
quantity  of  the  fuel,  as  a  pound  or  a  cubic  foot,  will  give  up  when 
burned.* 

The  British  thermal  unit  is  equivalent  to  778  foot-pounds  of 

*  For  higher  and  lower  heat  values,  and  methods  of  -determining,  see 
chapter  on  Combustion  and  Heat  Values. 

276 


ECONOMY  AND  EFFICIENCY  277 

mechanical  energy  transformed  into  heat,  as  by  friction  between 
two  solid  bodies.     This  is  the  generally  accepted  value. 

If  mechanical  energy  is  transformed  into  heat  at  the  rate  of  one 
horsepower  during  a  period  of  one  hour,  the  amount  of  heat 
produced  will  be  1,980,000  -f-  778  =  2545  B.t.u.  The  relation 
between  British  thermal  units  and  horsepower  per  hour,  horse- 
power per  minute,  and  horsepower  per  second,  can  therefore  be 
written,  for  convenience: 

One  h.p.-hour  =  2545  B.t.u. 
One  h.p.-min.  =      42.416  B.t.u. 
One  h.p.-sec.    =          .70694  B.t.u. 

187.  Motor  Economy  Defined.  —  It  is  of  course  desirable  to 
obtain  as  great  an  amount  of  mechanical  energy  from  a  given 
quantity  of  fuel  as  is  possible  under  suitable  conditions  of  opera- 
tion, thus  securing  the  greatest  economy  of  fuel  that  is  compatible 
with  conditions  exterior  to  the  motor.  Since  the  term  "economy 
of  fuel"  does  not  have  a  definite  meaning  when  applied  to  the 
internal-combustion  motor,  for  the  reason  that  a  gas  producer 
may  be  sometimes  included  in  this  economy  and  at  other  times 
not  included,  it  is  advisable  to  use  the  term  motor  economy  when 
dealing  with  the  motor  only. 

The  unqualified  terms  fuel  economy  of  motor  and  motor 
economy  will  be  taken  to  mean  either  the  amount  of  fuel  or  the 
heat  value  of  all  the  fuel  that  is  supplied  to  the  motor  per  delivered 
horsepower  per  hour  (D.h.p.  or  B.h.p.  hour).  The  amount  of  fuel 
may  be  expressed  in  different  ways,  as  pounds  of  coal,  cubic  feet 
of  gas,  pounds  of  combustible,  British  thermal  units,  etc. 

Motor  economy  does  not  have  any  assumed  conditions  under 
which  the  delivered  mechanical  energy  is  equal  to  the  equivalent 
heat  energy  of  the  fuel  that  it  receives. 

If  a  motor  is  operating  on  suction  producer  gas  and  drawing 
the  gas  through  and  from  the  producer  by  its  own  power,  it  will 
require  more  pounds  of  fuel  gas  to  deliver  a  horsepower  than  if 
the  motor  received  the  same  gas  at  atmospheric  pressure  or  from 
gas  mains  at  a  pressure  higher  than  atmospheric.  More  power 
is  required  to  pump  or  draw  the  gas  through  the  producer  into  the 


278  THE  GAS  ENGINE 

motor  than  from  the  atmosphere  direct.  This  additional  power 
must  be  furnished  by  a  part  of  the  mechanical  energy  produced 
by  the  combustion  of  the  gas  in  the  motor. 

1 88.  Motor  Efficiency  Defined.  —  The  measure  of  the  economy 
of  the  motor  is  the  ratio  between  the  amount  of  energy  that  it 
delivers  during  a  specified  time  and  the  amount  of  energy  that  is 
supplied  by  the  fuel  during  the  same  time.  The  former  is  equal 
to  the  product  obtained  by  multiplying  the  rate  of  working 
(D.h.p.)  by  the  time  of  working.  The  two  quantities  of  the  ratio 
must  be  expressed  in  the  same  units.  This  can  be  done  by  multi- 
plying the  delivered  horsepower  hours  by  the  value  of  one  horse- 
power-hour =  2545  British  thermal  units. 

The  following  are  convenient  forms  for  expressing  the  effi- 
ciencies : 

2545  (D.h.p.)  hours 

Motor  efficiency  =      ^  v  e    „/  1 :> 

B.tu.  of  all  fuel  used 

or 

2545 


Motor  efficiency 


B.t.u.  of  fuel  used  per  h.p.  per  hour 


in  both  of  which  the  numerator  represents  the  number  of  B.t.u. 's 
that  are  equivalent  to  the  delivered  mechanical  energy. 

In  the  case  of  a  motor  whose  piston  diameter  =  n  inches, 
stroke  =  12  inches,  running  at  290  revolutions  per  minute,  and 
whose  guaranteed  fuel  economy  is  1200  B.t.u.  per  delivered 
horsepower  per  hour,  the 

2<545  X  1  X  1 

Motor  efficiency  =  -^—^ =  .212  =  21.2  per  cent. 

1200 

And  in  another  motor  whose  piston  diameter  =  18  inches, 
stroke  =  19  inches,  running  at  180  r.p.m.  and  guaranteed  to 
deliver  one  horsepower-hour  at  a  fuel  consumption  of  10.5  cubic 
feet  of  gas  whose  lower  heat  value  is  1050  B.t.u.  per  cubic  foot 
at  the  temperature  and  pressure  at  which  the  gas  is  delivered  to 
the  motor,  the 

Motor  efficiency  =  2§S =  .231  =  23.1  percent. 

10.5  X  1050 


ECONOMY  AND  EFFICIENCY  279 

Another  motor  with  piston  diameter  =  8.5  inches,  stroke  = 
12.75  inches,  running  at  300  r.p.m.,  is  guaranteed  to  run  10  hours 
on  full  load  of  17  h.p.  (D.h.p.)  with  a  total  consumption  of  17 
gallons  of  commercial  gasoline. 

The  heat  value  of  gasoline  has  not  been  accurately  determined 
on  account  of  difficulty  in  getting  accurate  calori  metric  results. 
Neither  is  the  heat  value  the  same  for  all  gasoline.  It  probably 
lies  between  18,000  and  21,000  B.t.u.  per  pound.  The  specific 
gravity  of  gasoline  is  different  for  the  different  grades.  It  may 
be  taken  as  .65  for  this  case.  The  weight  of  a  gallon  of  pure 
water  at  a  temperature  of  62°  F.  is  8.3356  pounds.  The 
weight  of  a  gallon  of  gasoline  at  62°  F.  closely  approximates 
.65  X  8.3356  =  5.42  pounds.  Taking  the  heat  value  of  the 

gasoline  as  20,000  B.t.u.,  the 

« 

2545  X  17  X  10 

Motor  efficiency  =  —        -  -  -  =.2347  =  23.47  per  cent. 
17  X  5.42  X  20,000 

A  quite  commonly  accepted  standard  of  fuel  economy  of  small 
motors  is  one  pint  of  gasoline  per  horsepower  per  hour.  A  pint 
of  gasoline  weighs  about  .678  pounds  at  62°  F.  If  the  heat  value 
is  taken  as  20,000  B.t.u.  per  pound,  then  the 


Motor  efficiency  =  -—  -  -    '•  —  •  =  .1877  =  18.77  Per  cent- 
.678  X  20,000 

If  the  heat  value  of  the  gasoline  is  taken  at  18,000  B.t.u.  per 
pound,  then  the 

2545  X  1  X  1 

Motor  efficiency  =  ~^—^  -    —  •  =  .208=;  =  20.85  per  cent. 
.678  X  18,000 

Under  favorable  conditions  large  gas  engines  reach  a  motor 
efficiency  as  high  as  30  per  cent,  corresponding  to  a  fuel  economy 
of  8480  B.t.u.  per  brake  horsepower  (delivered  horsepower)  per 
hour. 

189.  Impulse-Output  Efficiency.  —  The  mechanical  power 
that  the  motor  delivers  (D.h.p.),  which  may  be  called  the  output 
of  the  motor,  is  what  remains  of  the  indicated  impulse  power 


280  THE  GAS  ENGINE 

(I.h.p.I)  after  deducting  from  it  (a)  the  power  lost  on  account  of 
the  mechanical  friction  of  the  motor,  (b)  the  power  required  to 
pump  or  force  the  charge  into  the  combustion  cylinder,  and  (c) 
possibly  some  other  small  consumption  of  power  such  as  that  for 
driving  an  oil  pump.  The  latter  would  generally  be  taken  as 
part  of  the  mechanical  friction  of  the  motor. 

The  impulse-output  efficiency  is  the  ratio  of  the  output  to  the 
indicated  horsepower  as  determined  from  the  impulse  loop  of 
the  indicator  diagram.  The  equation  for  it  is 

Impulse-output  efficiency  =  -    — —  • 

I.h.p.I 

This  ratio  is  sometimes  called  the  mechanical  efficiency  of  the 
motor,  but  this  seems  hardly  correct,  since  the  value  of  the  ratio 
is  changed  by  variation  of  the  pressure  at  which  the  fuel  gas  is 
received,  or  drawn  to  the  intake  of  the  motor.  Thus  the  ratio 
has  a  different  value  when  the  gas  is  drawn  through  a  suction 
producer  by  the  motor,  as  compared  with  its  value  when  the  gas 
is  received  at  atmospheric  pressure,  even  though  the  friction 
losses  in  the  motor  remain  unchanged. 

Applying  the  last  equation  to  a  motor  whose  piston  diameter 
=  6.75  inches  (piston  area  =  35.78  square  inches,  there  being 
no  piston  rod  in  the  combustion  chamber),  stroke  =  15.5  inches, 
running  at  260  r.p.m.  and  taking  126  charges  per  minute,  whose 
average  M.e.p.I  is  102  pounds  per  square  inch,  and  whose  D.h.p. 
=  15.32,  first  finding  the  I.h.p.I,  gives 

Ih     l_  (M.e.p.I)  ALY  _  102   X  45-7$  X  15.5  X  126  _  ^  ^ 

33,000  33)°°° 

and 

Impulse-output  efficiency  =  =  .846  =  84.6  per  cent. 

18.1 

190.  Mechanical  Efficiency  of  Motor.  —  The  mechanical 
efficiency  of  the  motor  is  the  ratio  of  the  output  (D.hp.)  to  the  net 
indicated  power  (I.h.p.N).  The  mean  effective  pressure  of  the 
pumping  diagram  of  the  motor  referred  to  in  the  preceding  section 


ECONOMY  AND  EFFICIENCY  281 

is  too  small  to  be  determined  accurately,  and  no  low-spring  card 
was  taken.  It  will  be  assumed  that  the  mean  effective  pressure 
of  the  pumping  card  (M.e.p.R)  =  two  pounds  per  square  inch. 
The  M.e.p.I  is  102  pounds  per  square  inch.  Therefore  the 
M.e.p.N  =  102  —  2  =  100  pounds  per  square  inch.  The  net 
indicated  horsepower  is 

X 

(M.e.p.N)  ALY      100  X  45.78  X  15.5  X  126 

I.h.p.N  =  = =  17-74, 

33>°°°  33  >°°°     . 

and  the 

Mechanical  efficiency  =  — — -  =  =.864  =  86.4  per  cent. 

I.h.p.N      17.74 

This  is  but  slightly  different  from  the  impulse-output  efficiency, 
but  in  a  case  like  that  shown  in  Fig.  77,  where  the  pumping 
loop  is  large,  there  is  a  very  marked  difference  between  the  two 
efficiencies. 

In  a  two-cycle  motor  the  average  rate  of  the  work  of  precom- 
pressing  the  charges  so  as  to  force  them  into  the  combustion 
cylinder  is  to  be  deducted  from  the  average  impulse  rate  of  working 
in  order  to  obtain  the  net  indicated  horsepower. 

191.  Thermodynamic  or  Thermal  Efficiency  of  the  Motor. — 
This  is  the  efficiency  of  transforming  heat  into  mechanical  energy. 
It  is  the  ratio  of  the  mechanical  energy  delivered  to  the  piston  to 
that  of  the  heat  energy  liberated  by  the  combustion  of  the  fuel, 
as  applied  to  a  combustion  motor.  Both  quantities  must  be 
expressed  in  the  same  unit  of  measure.  The  energy  delivered  to 
the  piston  is  that  of  the  impulse  stroke  as  determined  from  the 
impulse  loop  of  the  indicator  diagram.  Remembering  that  one 
horsepower-hour  equals  2545  British  thermal  units,  the  equation 
can  be  written, 

2<4<  (I.h.p.I)  hours 

Therm,  efficiency  =     3  *  ^ — > 

B.t.u.  of  all  fuel  used 

or 

2545 


Therm,  efficiency 


B.t.u.  of  all  fuel  used  per  I.h.p.I  per  hr. 


282  THE  GAS  ENGINE 

in  both  of  which  B.t.u.  represents  the  amount  of  heat  given  up  by 
the  fuel  to  produce  the  mechanical  energy  represented  by  the 
numerator  of  the  fraction. 

Applied  to  a  motor  whose  impulse  loop  of  the  diagram  repre- 
sents twenty  horsepower  (20  h.p.)  and  which  operates  on  1.7  gal- 
lons of  gasoline  per  hour,  taking  the  heat  value  of  the  gasoline 
as  20,000  B.t.u.  per  pound  and  the  weight  as  5.42  pounds  per 
gallon,  the 

2545  X  20  X  1 

Therm,  efficiency  =  =  .276  =  27.6  per  cent. 

1.7  X  5.42  X  20,000 

In  a  motor  with  piston  diameter  =  15.185  inches,  stroke  — 
1 8  inches,  running  at  175  r.p.m.  per  minute  with  an  indicated 
horsepower  (I.h.p.I)  =  75  and  a  delivered  horsepower  (D.h.p.) 
=  65.1,  using  10.5  cubic  feet  of  gas  having  a  heat  value  of  1050 
B.t.u.  per  cubic  foot,  the 

Therm,  efficiency  =  — =  .266  =  26.6  per  cent. 

65.1  X  10.5  X  1050 

192.  Plant  Economy  and  Efficiency.  —  In  the  case  of  a  suction 
gas  producer  operating  in  connection  with  an  internal-combustion 
motor,  when  the  power  plant  is  entirely  self-contained  and  there 
is  no  demand  for  power  or  fuel  from  outside  the  plant  to  operate 
auxiliary  apparatus,  the  fuel  economy  of  the  plant  may  be  expressed 
as  the  amount  of  fuel  fed  to  the  producer  per  delivered  horsepower 
per  hour.  The  amount  of  fuel  may  be  stated  as  pounds  of  coal, 
or  pounds  of  combustible,  etc.,  per  horsepower  per  hour. 

If  fuel  is  used  outside  the  producer  for  operating  auxiliary 
apparatus,  then  the  total  amount  of  fuel,  or  of  combustible,  etc., 
must  be  taken  into  consideration  in  stating  the  economy  of  the 
plant.  When  steam  or  mechanical  or  electrical  energy  from 
some  exterior  source  is  used,  and  the  fuel  for  developing  the 
power  or  generating  the  steam  cannot  be  determined,  then  the 
value  of  the  external  energy  in  foot-pounds  or  B.t.u.  may  be 
taken  as  a  basis  for  determining  the  equivalent  amount  of  fuel 
that  would  have  to  be  used  if  the  power  were  generated  from 


ECONOMY  AND  EFFICIENCY  283 

fuel  at  the  plant  under  consideration.  The  details  of  the  vari- 
ous steps  depend  so  much  on  the  conditions  existing  that  it  is 
hardly  possible  to  give  any  general  statement  of  the  method  to  be 
followed  other  than  that  the  efficiency  of  the  transformation  of 
the  heat  energy  into  mechanical  energy  may  be  taken  the  same 
as  that  of  the  complete  plant  as  nearly  as  this  efficiency  can  be 
determined. 

The  efficiency  of  a  self-contained  plant  is  the  ratio  of  the 
delivered  horsepower  for  any  specified  period  of  time  to  the  heat 
value  of  the  fuel  fed  to  the  producer  during  the  same  period. 
And  when  all  the  power  used  for  the  motor  and  auxiliary  apparatus 
is  generated  from  fuel  whose  amount  can  be  directly  deter- 
mined, the  efficiency  is  the  ratio  of  the  power  delivered  to  the  heat 
value  of  the  fuel  used.  For  these  two  cases  the  mathematical 
expression  of  the  efficiency  is 

2545  X  D.h.p.  X  hours 

Plant  efficiency  =  -*22 £ , 

B.t.u.  of  all  fuel  used 

or 

2545 


Plant  efficiency 


B.t.u.  of  all  fuel  used  per  D.h.p.  per  hr. 


193.  Comparison  of  Efficiencies.  —  In  comparing  motors  with 
regard  to  either  their  motor  efficiency,  impulse-output  efficiency, 
or  their  thermodynamic  efficiency,  and  also  in  comparing  plant 
efficiencies,  it  should  be  carefully  observed  that  corresponding 
heat  values  of  the  fuel  are  used  in  all  cases.  Either  the  higher 
heat  values  should  be  used  for  all  cases  or  the  lower  heat  values 
should  be  used  for  all. 

A  discussion  of  heat  values  is  taken  up  in  the  chapter  on 
Combustion  and  Heat  Values, 


CHAPTER  XVI. 
PHYSICAL  PROPERTIES   OF  GASES. 

194.  Introductory  to  the  matter  to  follow,  some  of  the  laws  of 
perfect  (or  assumed  to  be  perfect)  gases  will  be  stated.     These 
are  the  laws  which  some  of  the  actual  gases  follow  more  or  less 
closely,  and  which  a  "perfect"  gas  would  follow  absolutely  if 
such  a  gas  were  existent. 

Within  certain  limited  ranges  of  temperature  not  greatly 
removed  from  atmospheric  conditions,  the  actual  gases  follow 
the  laws  of  a  perfect  gas  with  sufficient  accuracy  to  allow  them  to 
be  considered  perfect  gases  for  the  purposes  of  this  work.  This 
does  not  apply  to  temperatures  as  high  as  those  of  combustion, 
or,  in  some  cases,  even  as  high  as  the  temperatures  produced  by 
compression  in  the  combustion  motor. 

At  temperatures  as  high  as  those  at  which  the  burned  gases  are 
discharged  from  a  combustion  motor,  the  actual  gases  depart  so 
far  from  the  laws  of  a  perfect  gas  that  any  assumption  that  they 
follow  the  perfect  gas  laws  even  approximately  will  lead  to  totally 
erroneous  results. 

195.  Density  and  Weight  of  Gases.  —  The  density  of  a  gas  is 
its  heaviness  or  weight  referred  to  some  standard.     The  standard 
may  be  another  gas  whose  density  is  taken  as  unity,  or  a  unit 
of  weight  used   in   connection   with   a  unit  volume.     For  the 
present  purpose  it  is  convenient  to  express  the  density  in  pounds 
per  cubic  foot. 

The  specific  volume  of  a  gas  is  the  space  occupied  by  a  given 
weight  or  mass  of  it.  It  will  be  expressed  in  cubic  feet  per 
pound.  The  specific  volume  in  cubic  feet  per  pound  is  equal  to 
the  reciprocal  of  the  weight  in  pounds  per  cubic  foot. 

Since  changes  in  temperature  and  pressure  affect  the  volume 
of  a  given  weight  of  gas,  the  density  and  specific  volume  must  be 
given  with  reference  to  a  definite  temperature  and  pressure. 

284 


PHYSICAL  PROPERTIES  OF  GASES 


28S 


TABLE   I. 

DENSITY  AND  SPECIFIC  VOLUME  OF  GASES. 
14.7  Ibs.  per  sq.  in.  =  2116.8  Ibs.  per  sq.  ft.  pressure. 


Name. 

Chemical 
Form. 

Density. 
Lbs.  per  Cu.  Ft. 

Specific  Volume. 
Cu.  Ft.  per  Lb. 

32°  F. 

62°  F. 

32°  F. 

62°  F. 

Oxygen  

02 

N2 
C02 

H2 
CO 

.0893 
.0785 
.1227 
.0807 
.0056 
.0780 

.0841 

•0739 
.1156    ' 

.07612 
.00528 
.0736 

1  1.  20 
12.73 

8.15 
12.39 
178.2 
12.82 

11.90 

13-53 
8.6S 

I3-I4 
189.4 
13.61 

Nitrogen 

Carbon  dioxide    

Air  

Hydrogen 

Carbon  monoxide  

Methane  or  marsh  gas  .... 

CH4 

.0447 

.0421 

22.39 

23-75 

Ethylene  or  olefiant  gas  .  .  . 
Propylene 

C2H4 
C3H6 
C6H6 

.0780 
.  1172 
.2173 

•°735 
.  1104 
.2048 

12.82 

8-53 
4.60 

13.60 
9.06 

4.88 

Benzene  vapor  or  benzol  .  * 

*  This  is  not  the  benzine  from  petroleum. 

In  Table  I  the  densities  and  specific  volumes  of  the  gases  with 
which  the  combustion  motor  is  most  concerned  are  given  for 
atmospheric  pressures  and  temperatures  of  32°  F.  and  62°  F. 

196.  Laws  of  a  Perfect  Gas.  —  A  perfect  gas  is  one  which  in 
passing  through  changes  of  temperature,  pressure,  and  volume, 
behaves  in  accordance  with  the  following  laws,  using  absolute 
temperatures  and  pressures : 

Pressure  varies  inversely  as  the  volume  when  the  temperature 
is  constant.  (Law  of  Mariotte  and  Boyle. ) 

Pressure  varies  directly  as  the  absolute  temperature  when  the 
volume  is  constant. 

Volume  varies  directly  as  the  absolute  temperature  when  the 
pressure  is  constant.  (Law  of  Charles.) 


286  THE  GAS  ENGINE 

*  Specific  heat  (per  unit   weight)    is   constant  for   all   tem- 
peratures   and    pressures.       This    refers    to    both   the  specific 
heat  of  constant  volume  and  the  specific  heat  of  constant  pres- 
sure.    The  values  of  these  specific  heats  are  different  for  any 
gas,   but   each   has  its  own   constant  value    peculiar    to  that 
perfect  gas. 

The  absolute  pressure  zero  is  about  14.7  pounds  per  square 
inch  below  atmospheric  pressure  near  sea  level,  f 

The  zero  of  absolute  temperature  is  about  459  degrees  below 
the  ordinary  Fahrenheit  zero  (—  459°  F.).  To  obtain  the  abso- 
lute temperature  corresponding  to  any  reading  of  the  Fahrenheit 
thermometer,  459  degrees  must  be  added  to  the  reading. 

Absolute  temp.  Fahr.  =  Thermometer  reading  +  459°  F. 

The  volume  change  of  a  perfect  gas  for  each  Fahrenheit  degree 
change  of  temperature  (at  any  temperature)  is  ^y  of  its  volume 
at  32°  F.  when  the  pressure  remains  constant.  If  the  volume  of 
the  gas  at  32°  F.  is  491  cubic  feet,  then  at  31°  F.  it  will  be  490 
cubic  feet;  at  22°  F.  481  cubic  feet;  at  zero  F.  by  the  ther- 
mometer it  will  be  459  cubic  feet;  and  at  —  459°  F.,  which  is 
the  absolute  zero,  its  volume  will  be  zero  theoretically  for  the 
perfect  gas. 

At  a  temperature  of  33°  F.  the  volume  of  the  gas  will  be  492 
cubic  feet;  at  62°  F.  it  will  be  491  +  (62  —  32)  =  491  -f  30  = 
521  cubic  feet. 

The  pressure  change  of  a  perfect  gas  for  each  Fahrenheit  degree 
change  of  temperature  (at  any  temperature)  is  ¥|T  of  its  pressure 
at  32°  F.  when  the  volume  remains  constant.  The  pressure  at 
absolute  zero  is  therefore  zero. 

*  The  term  "specific  heat"  without  further  qualification  is  understood  to 
mean  the  specific  heat  of  unit  weight.     Volumetric  specific  heat  is  also  used. 
The  latter  is  the  specific  heat  of  unit  volume  and  is  variable  with  changes  of 
temperature  and  pressure  if  the  specific  heat  per  unit  weight  is  constant,  or 
in  any  case  except  where  the  specific  heat  per  unit  weight  varies  inversely 
as  the  temperature  and  pressure. 

f  A  sufficiently  accurate  approximation  of  the  decrease  of  pressure  with 
increase  of  altitude,  for  the  present  purpose,  is  one-half  pound  per  square  inch 
decrease  of  pressure  for  each  1000  feet  of  altitude. 


PHYSICAL  PROPERTIES  OF  GASES 


287 


The  above  laws  of  a  perfect  gas  may  be  expressed  mathe- 
matically as  follows: 


p. 


F, 
Vi 

v\ 
Vn 


p_ 
p, 

P.V, 


For  constant  volume. 


For  constant  pressure. 


For  constant  temperature. 


In  each  of  these  equations  the  sume  subscript  indicates  coin- 
cident values,  and  the  notation  is : 

P  =  absolute  pressure.     (The  zero  pressure  is  at  14.7  Ibs.  per 

sq.    in.  =  2116. 8   Ibs.   per   sq.  ft.  below   atmospheric 

pressure  at  sea  level); 
V  =  volume; 
T  =  absolute    temperature.     (The    zero    temperature    is    at 

—459°  F.,  which  is  491°  F.  below  the  freezing  point  of 

water  at  atmospheric  pressure); 
Pv  Vv  7\=  the  initial  condition; 
P2,  F2,  T2  =  the  changed  or  final  condition. 

And,  in  accordance  with  the  laws  of  a  perfect  gas, 

P  V        T 

*  \v  i  _  •*•  i 

P  V        T 

r2V 2  ^2 

197.  Example.  —  Find  the  weight  of  a  cubic  foot  of  air  at  a 
temperature  of  102°  F.  and  a  pressure  of  20  pounds  per  square 
inch  absolute. 

In  Table  I  the  density  in  pounds  per  cubic  foot  is  given  for 
both  32°  F.  and  62°  F.  at  14.7  pounds  per  square  inch  absolute 


288  THE  GAS  ENGINE 

pressure.  The  air  can  be  reduced  to  its  equivalent  volume  at 
either  of  these  temperatures  and  its  weight  obtained  by  multiply- 
ing the  volume  at  that  temperature  by  the  weight  per  cubic  foot 
at  the  same  temperature.  The  temperature  of  62°  F.  will  be 
taken  as  that  at  which  the  equivalent  volume  is  to  be  found. 
The  given  quantities  are: 

Initial  volume  =  1  cu.  ft. ; 

Initial  temp.     =  102°  F.  =  102  +  459  =  561°  absolute  F.; 

Initial  pres.       =  20  Ibs.  per  sq.  in.  absolute; 

Final  temp.       =  62°  F.  =  62  +  459  =  521°  absolute  F.; 

Final  pres.        =14.7  Ibs.  per  sq.  in.  absolute. 

The  computations  will  be  made  in  two  steps  by  first  finding 
the  change  of  volume  due  to  the  change  of  temperature  at  constant 
pressure  and  then  the  change  of  volume  due  to  change  of  pressure 
at  constant  temperature. 

The  equations  of  section  196  can  be  applied.  The  subscript 
1  will  be  taken  to  represent  the  initial  conditions  for  the  change 
under  consideration  for  the  moment,  and  the  subscript  2  to  repre- 
sent the  final  condition  of  the  same  change. 

The  equation  for  the  change  at  constant  pressure,  modified  in 
form  for  convenience,  is 


»v- 


The  substitution  of  the  initial  values  in  this  equation  gives 

_  1X521  =  cu  ft 

56i 

at  62°  F.  and  20  pounds  per  square  inch  pressure. 

The  equation  for  the  change  of  pressure  and  volume  at  constant 
temperature,  modified  in  form  for  convenience,  is 


PHYSICAL  PROPERTIES  OF  GASES  289 

The  initial  volume  to  be  substituted  in  this  c#se  is  the  .928 
cubic  foot  obtained  by  the  last  computation.  By  substituting 
this  and  the  other  quantities  in  the  last  equation  it  becomes 

.928  X  20 

F2  =  -  —  =  1.26  cu.  ft, 

14.7 

which  is  the  volume  at  62°  F.  and  14.7  pounds  per  square  inch 
pressure. 

The  weight  of  air  at  this  temperature  and  pressure,  as  given 
in  Table  I,  is  .07612  of  a  pound  per  cubic  foot.  The  weight 
of  a  cubic  foot  of  air  at  the  given  temperature  of  102°  F.  and 
pressure  of  20  pounds  per  square  inch  absolute,  is  therefore 

1.26  X  .07612  =  .096  Ib. 

Instead  of  making  the  computations  in  two  steps,  as  above,  for 
reducing  a  cubic  foot  of  gas  at  the  observed  temperature  and 
pressure  to  its  equivalent  volume  at  62°  F.  and  14.7  pounds  per 
square  inch  pressure,  the  reduction  can  be  made  direct  by  the  last 
equation  of  section  196.  This  equation,  after  transposing  to  a 
suitable  form  for  application,  is 


Whence,  by  substitution, 

20  X  1  X  521 

F,  =  -  =  1.26  cu.  ft, 

14.7  X  561 

198.  The  specific  heat  of  a  gas  (per  unit  weight)  is  the  amount 
of  heat  required  to  raise  the  temperature  one  degree.  It  is  often 
given  for  two  different  conditions,  one  for  constant  pressure  and 
the  other  for  constant  volume.  It  is  convenient  for  the  present 
purpose  to  express  the  specific  heat  in  British  thermal  units  per 
pound  of  gas. 


THE  GAS  ENGINE 


TABLE    II. 

SPECIFIC  HEATS  OF  GASES. 

For  Atmospheric  Temperatures. 


Gas. 

Chem- 
ical 
Form. 

Specific  Heat.      Can  be  taken  as 
B.t.u.  per  Lb. 

Per  Pound. 

Per  Cu.  Ft.  at 
14.7  Lbs.  per  Sq.  In. 

Con- 
stant 
Pres- 
sure. 

Con- 
stant 
Vol- 
ume. 

Constant 
Pressure. 

Constant 
Volume. 

32°  F. 

62°  F. 

32°  F. 

62°  F. 

Oxygen          

02 

N2 
C02 

•2175 
.2438 
.2170 

•2375 
3-409 
.2479 

•5929 
.4040 

•155 

•173 
.171 
.169 
2.406 

•173 
.467 

•332 

.0194 
.0191 
.  0266 
.0192 
.0191 
.0195 
.0265 
•0343 

.0183 
.0180 
.0251 
.0181 
.0180 
.0182 
.0250 
.0297 

.0138 
.0136 

.0210 
.0136 
•0135 
•°I35 
.0209 
.0259 

.0130 
.0128 
.0198 
.0127 
.0127 
.0127 
.0197 
.0244 

Nitrogen  
Carbon  dioxide  

Air 

Hydrogen  

H2 
CO 
CH4 
C2H4 

Carbon  monoxide  
Methane  or  marsh  gas  
Ethylene  or  olefiant  gas  

The  specific  heat  of  constant  volume  (by  weight)  is  the  amount 
of  heat,  in  British  thermal  units,  that  must  be  given  to  a  pound 
of  gas  to  raise  its  temperature  one  degree  Fahrenheit  while  the 
volume  remains  unchanged.  This  corresponds  to  adding  a 
B.t.u.  of  heat  to  a  pound  of  gas  enclosed  in  a  vessel  of  fixed  volume 
whose  walls  are  impermeable  to  heat. 

The  specific  heat  of  constant  pressure  (by  weight)  is  the  amount 
of  heat  that  must  be  given  to  a  pound  of  the  gas  to  raise  its  tem- 
perature one  degree  Fahrenheit  while  the  pressure  remains  con- 
stant. This  corresponds  to  heating  the  gas  in  a  vertical  cylinder 
with  a  free  frictionless  piston  closing  the  upper  end,  whose  weight 
determines  the  gaseous  pressure.  When  heat  is. added  to  the 
gas  its  temperature  rises  and  it  expands  so  as  to  lift  the  piston 


PHYSICAL  PROPERTIES  OF   GASES  291 

against  the  constant  resistance  of  the  weight  of  the  piston  (and 
also  against  atmospheric  pressure  if  the  latter  acts  •on  the  exposed 
side  of  the  piston),  which  gives  a  constant  gas  pressure. 

The  specific  heat  of  constant  pressure  is  greater  than  that  of 
constant  volume.  At  constant  volume  only  enough  heat  is  added 
to  raise  the  temperature,  but  at  constant  pressure  there  must  be 
enough  heat  added  not  only  to  increase  the  temperature  but  also 
to  do  the  work  of  expanding  the  gas,  as  in  the  case  of  lifting  the 
piston,  just  mentioned. 

The  specific  heats  just  mentioned  can  be  taken  as  practically 
constant  for  atmospheric  temperatures.  But  for  the  high  tem- 
peratures of  combustion  the  specific  heat  has  been  found  to 
increase  rapidly  with  increase  of  temperature.  Variation  of 
pressure,  dealing  with  pressures  as  high  as  those  of  the  combustion 
motor,  also  causes  variation  of  the  specific  heats. 

199.  Example.  —  Find  the  amount  of  heat  necessary  to  raise 
the  temperature  of  3  pounds  of  carbon  monoxide   (CO)  from 
32°  F.  to  62°  F.  at  atmospheric  pressure. 

This  is  a  case  of  change  of  temperature  at  constant  pressure. 
The  specific  heat  of  constant  pressure  for  CO  is  given  in  Table  II 
as  .248  B.t.u.  per  pound.  The  amount  of  heat  required  to  raise 
the  temperature  as  stated  is 

3  (62  -  32)  .248  =  3  X  30  X  .248  =  22.32  B.t.u. 

200.  Volumetric  Specific  Heat.  —  It  is  sometimes  convenient 
to  use  the  amount  of  heat  that  will  change  the  temperature  of  a 
unit  volume  (as  a  cubic  foot)  of  gas  one  degree. 

The  volumetric  specific  heat  of  a  cubic  foot  of  gas  at  any  tem- 
perature and  pressure  can  be  found  by  multiplying  the  specific 
heat  of  the  gas  in  British  thermal  units  per  pound  of  the  gas  by 
the  weight  of  the  gas  per  cubic  foot  at  the  temperature  and 
pressure  taken.  The  specific  heat  by  weight  must  be  that  for 
the  temperature  and  pressure  at  which  the  gas  is  taken.  The 
volumetric  specific  heat  is  really  the  specific  heat  of  a  weight  of 
gas  determined  by  the  pressure  and  temperature.  It  is  not  the 
same  at  different  temperatures  or  at  different  pressures. 

In  Table  II  the  specific  heats  of  the  more  important  fuel  gases 


292  THE   GAS  ENGINE 

for  the  "combustion  motor,  and  of  the  products  of  combustion, 
are  given  in  British  thermal  units  per  pound  and  also  per  cubic 
foot  for  temperatures  of  32°  F.  and  62°  F.  at  atmospheric  pres- 
sure. 

201.  Example.  —  Find  the  heat  required  to  raise  the  tem- 
perature of  3  cubic  feet  of  carbon  monoxide  (CO)  from  32°  F.  to 
62°  F.  at  atmospheric  pressure.  The  volumetric  specific  heat  of 
CO  is  given  in  the  table  as  .0195  B.t.u.  per  cubic  foot  for  a  constant 
pressure  of  14.7  pounds  per  square  inch  pressure  and  at  a  tem- 
perature of  32°  F.  The  amount  of  heat  necessary  for  the 
required  change  is 

3  (62  -  32)  .0195  =  3  X  30  X  .0195  =  1.755  B.t.u. 

Example.  —  What  amount  of  heat  will  a  cubic  foot  of  CO  give 
out  while  cooling  from  62°  F.  to  32°  F.  at  atmospheric  pressure? 

The  volumetric  specific  heat  of  CO  at  62°  F.  and  14.7  pounds 
per  square  inch  pressure  is  given  in  the  table  as  .0182  for  con- 
stant pressure.  The  heat  given  out  during  the  change  will  be 

3  (62  -  32)  .0182  =  3  X  30  X  .0182  =  1.638  B.tu. 


CHAPTER  XVII. 
COMBUSTION  AND  HEAT   VALUES. 

202.   Combustion  and  Volumetric  Change  Due  to  Combustion. 

-  Combustion,  taken  in  the  broadest  sense,  is  the  chemical 
combination  of  elements  or  compounds  accompanied  by  the 
liberation  or  production  of  heat.  As  used  in  relation  to  the 
internal-combustion  motor  and  to  the  manufacture  of  com- 
bustible gases  from  solid  and  liquid  fuels  for  the  motor,  com- 
bustion means,  as  has  been  previously  stated,  the  chemical  union 
of  oxygen  with  the  carbon,  hydrogen,  or  other  chemical  elements 
and  compounds  in  the  fuel.  Carbon,  hydrogen,  the  hydrocar- 
bons (which  are  numerous  compounds  of  hydrogen  and  carbon 
in  different  proportions),  and  carbon  monoxide  are  practically 
all  the  fuels  that  are  considered,  however. 

The  volume  of  the  gaseous  products  of  combustion  differs  in 
many  cases  from  that  of  the  combustible  mixture  that  is  burned 
when  both  the  combustible  mixture  and  the  gaseous  products  of 
combustion  are  brought  to  and  compared  at  the  same  temperature 
and  pressure.  In  some  cases  there  is  a  decrease  of  specific 
volume  due  to  combustion,  in  others  an  increase,  and  in  still 
others  no  change  of  specific  volume. 

If  hydrogen  and  oxygen  are  chemically  combined  by  burning, 
the  volume  of  the  steam  formed  is  less  than  that  of  the  mixture  of 
hydrogen  and  oxygen  before  combustion,  both  taken  at  the  same 
temperature,  as  just  stated.  This  is  shown  by  the  following 
chemical  equation,  which  deals  with  molecular  quantities. 

2   VOl.  I    VOl.  2    VOl. 

2  H2  +  O2  =  2  H2O         (Hydrogen.     Contraction  =  ^-.) 

The  same  contraction  is  shown  in  the  combustion  of  carbon 
monoxide  burned  to  carbon  dioxide,  as  follows : 

2    VOl.         I    VOl.          2    VOl. 

2  CO  +  02  =  2  CO2      (Carbon  monoxide.     Contraction  =  ^.) 

293 


294  THE   GAS  ENGINE 

In  both  the  above  cases  three  volumes  of  the  combustible 
mixture  (two  volumes  of  hydrogen  and  one  of  oxygen  in  the  first 
case,  and  in  the  second  case  two  volumes  of  carbon  monoxide  and 
one  of  oxygen)  produce  two  volumes  of  gas  by  burning.  The 
volume  of  the  burned  gases  is  only  two- thirds  that  of  the  mixture 
in  each  case. 

But  in  the  combustion  of  marsh  gas  (methane)  there  is  no 
change  of  volume,  and  the  same  is  true  of  ethylene  (olenant  gas), 
as  shown  in  the  two  following  equations. 

i  vol.        2  vol.       i  vol.          2  voK 

CH4  +  2  O2  =  C02  +  2  H2O    (Methane.    Volume  change  =  o.) 

1  vol.     3  vol.        2  vol.  2  vol. 

C2H4  +  3  02=  2  C02+  2  H20   (Ethylene.    Volume  change  =  o.) 

In  each  of  the  last  two  cases  three  volumes  of  the  combustible 
mixture  produce  three  volumes  of  the  burned  gases. 

Propylene  and  benzol  both  show  an  increase  of  volume  in  the 
products  of  combustion,  as  the  following  two  equations  indicate. 

2  vol.         9  vol.        6  vol.          6  vol. 

2  C3H6+  gO2=  6C02+  6H20    (Propylene.    Expansion  =  T1T.) 

2  vol.          15  vol.        12  vol.          6  vol. 

2  C6H6+  15  O2  =  12  C02  +  6  H20     (Benzol.    Expansion  =  iV-) 

Contraction  of  volume,  at  equal  temperatures  and  pressures, 
by  combustion  has  the  effect  of  reducing  the  pressure  that  would 
be  produced  by  combustion  if  there  were  no  contraction  of 
volume.  The  indicator  diagram  takes  into  account  such  varia- 
tion of  volume  by  combustion.  The  reduction  of  volume  is  not 
as  great  when  air  is  used  to  furnish  the  oxygen  for  combustion 
as  is  shown  by  the  above  equations,  which  deal  only  with  the 
chemically  active  constituents  of  the  combustible  mixture.  The 
residual  inert  (burned)  gases  in  the  motor  cylinder  also  help  to 
reduce  the  ratio  of  contraction.  There  is  therefore  a  certain 
advantage,  in  relation  to  contraction,  in  having  the  combustible 
mixture  diluted  with  the  nitrogen  of  the  air  and  by  the  inert 
residual  gases  of  a  preceding  combustion. 

There  is  also  an  advantage  in  the  dilution  of  the  combustible 


COMBUSTION  AND  HEAT  VALUES  295 

mixture  on  account  of  keeping  down  the  temperature  of  the 
products  of  combustion  in  view  of  the  fact  that  the  specific  heat 
increases  rapidly  with  the  rise  of  temperature  for  temperatures  as 
high  as  those  of  combustion,  under  the  conditions  of  operation 
of  the  combustion  motor. 

203.  Complete  and  Incomplete  Combustion.  —  Complete  com- 
bustion is  the  combination  of  chemical  elements  in  the  proportion 
to  form  their  most  stable  compound. 

Incomplete  combustion  with  oxygen  is  the  process  of  the 
chemical  union  of  the  fuel  element  with  the  oxygen  in  a  proportion 
that  produces  a  compound  which  is  not  stable  in  the  presence  of 
more  oxygen  under  proper  conditions  for  adding  more  of  the 
oxygen  to  the  compound. 

As  an  example,  carbon  combines  with  oxygen  in  either  of  two 
proportions,  according  to  the  conditions  of  combustion,  to  form 
either  CO  or  CO2.  When  there  is  enough  oxygen  present,  CO2 
is  formed.  An  excess  of  oxygen  does  not  modify  this  proportion 
of  combination.  The  change  from  C  to  CO2  is  complete  com- 
bustion, for  if  the  CO2  is  heated  in  the  presence  of  more  oxygen 
it  will  not  combine  with  any  more  of  it. 

But  if  there  is  just  enough  oxygen  present  to  combine  with 
the  carbon  to  form  CO,  then  all  the  carbon  will  burn  to  CO. 
This  is  incomplete  combustion.  The  CO  is  not  a  stable  com- 
pound, for  if  it  is  mixed  with  more  oxygen  and  ignited,  all  or  part 
of  the  CO  will  burn  to  CO2  according  to  the  amount  of  free 
oxygen  present. 

If  there  is  more  than  enough  oxygen  present  with  the  carbon 
to  form  CO,  but  not  enough  to  form  CO2  of  all  the  carbon,  then 
burning  the  mixture  will  produce  both  CO  and  CO2  in  such  pro- 
portions as  will  take  up  all  the  oxygen.  This  action  is  also  called 
incomplete  combustion  in  engineering  practice. 

The  chemical  reactions  of  combustion  are  expressed  in  the 
following  atomic  equations: 

C     +  2  0  =  C02.     Complete  combustion  of  carbon. 
C     +     O  =  CO.     Incomplete  combustion  of  carbon. 
CO  +     0  =5  CO2.     Complete  combustion  of  CO. 


296  THE  GAS  ENGINE 

The  first  equation  represents  the  change  that  occurs  when 
coke  or  charcoal  is  burned  with  a  plentiful  supply  of  air  and  the 
temperature  of  the  fuel  is  kept  high,  as  indicated  by  a  white  heat. 
The  second  equation  indicates  the  change  if  there  is  but  a  scant 
supply  of  air  and  the  fuel  shows  only  a  red  heat.  The  third 
equation  is  the  expression  for  the  combustion  of  the  unstable 
product,  CO,  of  incomplete  combustion  of  carbon. 

204.  Heat  of  Combustion  is  Constant.  —  The  chemical  com- 
bination of  carbon  with  oxygen  in  the  proportion  to  form  carbon 
dioxide,  CO2,  always  liberates  the  same  amount  of  heat,  whether 
the  rate  of  combustion  is  rapid  or  slow.     The  amount  of  heat 
liberated  is  also  always  the  same  whether  the  combination  is 
made  directly  into  the  form  CO2,  or  first  into  CO  and  then  from 
CO  to  CO2.     The  heat  liberated  while  changing  from  C  to  CO 
is  always  a  fixed  amount,  and  so  is  that  for  the  combination  of  CO 
with  O  to  form  CO2.     The  sum  of  the  amounts  of  heat  produced 
during  the  last  two  steps  (C  to  CO  and  the  resulting  CO  to  CO2) 
is  equal  to  that  produced  during  the  direct  change  from  C  to  CO2. 

In  the  same  manner,  hydrogen  always  liberates  the  same 
amount  of  heat  when  combined  with  oxygen  to  form  water  vapor 
or  steam,  H2O.  The  other  combustible  elements  and  compounds 
follow  the  same  law. 

When  a  number  of  different  kinds  of  gases,  as  H,  CO,  CH4,  etc., 
are  mechanically  mixed  together,  as  in  the  case  of  power  gas  and 
illuminating  gas,  the  heat  liberated  by  the  combustion  of  the 
mixture  is  the  same  in  amount  as  if  each  constituent  (H,  CO, 
CH4,  etc.)  were  burned  separately  and  all  the  heat  thus  produced 
added  together.  This  does  not  apply  to  the  breaking  up  of  a 
chemical  compound  (such  as  CH4)  into  its  elements. 

205.  The  heat  value   or  calorific  power  of  a  fuel,  when  not 
qualified  more  definitely,  is  ordinarily  understood  to  mean  the 
amount  of  heat  that  is  liberated  by  burning  a  unit  weight  or  a 
unit  volume  of  the  fuel  and  bringing  the  temperature  and  pressure 
of  the  products  of  combustion  back  to  the  same  values  that  the 
fuel  and  the  supporter  of  combustion  (generally  air)  had  before 
ignition.     Since  it  is  practically  impossible  to  maintain  such  a 
final  pressure  and  temperature  during  the  burning  of  the  fuel  in 


COMBUSTION  AND  HEAT  VALUES 


297 


a  calorimeter,  the  necessary  corrections  in  the  readings  obtained 
are  made  to  secure  the  same  result  as  if  the  initial  and  final 
temperatures  and  pressures  had  been  the  same.  And  since  water 
is  used  in  the  calorimeter  to  take  up  the  heat  of  combustion,  both 
the  initial  and  final  temperatures  at  the  calorimeter  are  necessarily 
below  the  boiling  point  of  water.  The  water  vapor  produced  by 
combustion  when  hydrogen  is  present  is  therefore  condensed 
into  liquid  water. 

The  proportions  by  weight  in  which  the  fuel  and  oxygen  com- 
bine, the  weight  of  air  necessary  to  supply  the  required  oxygen 
when  air  is  used  in  accordance  with  the  method  of  commercially 
burning  any  fuel,  and  the  weight  of  the  resulting  products  of 
combustion  can  all  be  determined  by  the  aid  of  the  chemical 
equations  and  atomic  weights  of  the  chemical  elements.  In  the 
following  illustrative  equations,  the  atomic  weights  are  taken  for 
convenience  in  the  approximate  round  numbers  commonly  used 
for  such  purposes. 

TABLE    III. 

APPROXIMATE   ATOMIC  WEIGHTS. 


Substance  . 

Symbol. 

Atomic 
Weight. 

Carbon 

c 

12 

Hydrogen 

H 

I 

Oxvffen 

o 

16 

The  accurate  atomic  weight  of  hydrogen  as  reported  by  the  American  Chemical 
Society  is  1.008. 

The  relative  proportions  by  weight  in  which  CO  and  oxygen 
combine  are  shown  in  the  equation 

CO   +  0      =  C02 

28         1 6  44      Proportions  by  weight. 

When  one  pound  of  CO  is  burned  to  CO2,  the  weight  of  the 
oxygen  required  and  the  weight  of  the  products  of  combustion 
are  directly  obtained  by  dividing  the  above  equation  by  28 


298 


THE  GAS  ENGINE 


(which  is  the  weight  of  CO  burned  as  represented  in  the  above 
equation)  with  the  following  result. 

CO   +   0      =   C02 

Pounds.      i         .57  1.57 

When  the  oxygen  is  supplied  by  bringing  air  into  contact  with 
the  fuel,  the  weight  of  the  air  required  and  of  the  resulting  products 
is  obtained  in  a  similar  manner. 

Air  is  composed  chiefly  of  oxygen  and  nitrogen  in  the  propor- 
tion of  i  part  oxygen  and  3.326  parts  nitrogen  by  weight.  Water 
vapor  is  also  present  in  variable  amounts.  To  get  the  .57  pounds 
of  O  that  must  be  supplied,  there  must  be  4.326  X  .57  =  2.470 
pounds  of  air,  neglecting  moisture,  of  which  2.47  —  .57  =  1.9 
pounds  are  nitrogen.  The  nitrogen  remains  chemically  inert 
during  combustion.  The  chemical  equation  is 

CO     +       0  C02 

•57  i-57 

Pounds. 


2.47  Air.        3.47  Products. 

When  carbon  is  burned  to  CO2  the  equations  similar  to  the 
above  two  are 


and 


C     +  0 

12        16 

C        + 


-   CO 

28   Proportions  by  weight. 


0 


CO 


Pounds.  * 


i-33 
4-43  N 
5.76  Air. 


2-33 

4-43  N 

6.76  Products. 


The  additional  air  for  burning  the  products,  as  determined  in 
the  last  equation,  to  CO2,  and  the  resulting  final  products,  are 

CO     +       O      =  C02 

ir2.33  i-33  3-66 

Pounds,  j  4-43  N      4-43  N  8.86  N 

[6.76  5.76  Air.       12.52  Products. 


COMBUSTION  AND   HEAT  VALUES  299 

When  carbon  is  burned  directly  to  CO2  in  air,    • 


and 


C     -f 

12 

-2O   =   C02 

32           44 

Proportions 

C 

+             20 

C02 

f1 

Pounds,  j 

2.66 

8.86  N 

3.66 

8.86  N 

[  ii. 52  Air.       12.52  Products. 

By  adding  together  the  heat  of  burning  one  pound  of  carbon  to 
CO,  which  is  4206  B.t.u.,  and  that  of  burning  the  resulting  2^ 
pounds  of  CO  to  CO2  ,which  is  2^-  X  4476  =  10,444  B.t.u.,  the 
sum, 

4206  +  10,444  =  14)650  B.t.u., 

is  the  same  as  the  heat  produced  by  burning  the  pound  of  carbon 
direct  to  CO2. 

The  proportions  by  volume  for  the  burning  of  CO  with  O  are 
shown  in  the  following  molecular  equation. 

212     Volume  proportions. 
2  CO      +     02      =      C02 

56  32  88    Weight  proportions. 

The  burning  of  one  cubic  foot  of  CO  in  air  is  represented  in 
the  following  equation,  in  which  the  volumes  are  taken  at  62°  F. 
and  14.7  pounds  per  square  inch  pressure. 


\ 

2.39  Air. 

2.89  P: 

Cu.  ft. 

1 

1.89  N 

1.89  N 

I     i 

•5° 

I.OO 

CO 

+     0 

C02 

Pounds. 

.0736 

.0421 

•"57 

The  cubic  feet  of  oxygen  and  air  involved  in  burning  one  pound 
of  carbon  to  CO,  and  then  burning  the  resulting  CO  to  CO2,  are 
shown  in  the  next  two  equations. 


300 


THE  GAS  ENGINE 


Cu.  ft. 


Pounds, 


Cu.  ft. 


Pounds. 


75.8  Air. 

91.7  Products. 

60.0  N 

60.0  N 

. 

15.8 

3T-7 

C 

+     0 

CO 

I 

i-33 

2-33 

'91.7 

75.8  Air. 

151.7  Products. 

60.0 

N    60.0  N 

120.0   N 

.31-7 

15.8 

3*-7 

CO 

+  0 

=   C00 

3! 


For  one  pound  of  carbon  burned  direct  to  CO2  the  following 
applies : 

151.7  Air.       151.7  Products. 
Cu.  ft. 


I2O.O  N 


C        +        20 


Pounds. 


I2O.O  N 

31-? 
CO, 

->2 

3s 


And  for  one  pound  of  CO  burned  to  CO2: 

32.5  Air-          39-3  Products. 

Cu.  ft.     J  -  25.7  N  25.7  N 

[13.59        6.8  13.6 

CO     +      0  C02 

Pounds.      i  .C7  i  57 

+}  I  O  i 

Dealing  with  hydrogen  in  a  similar  manner,  the  equation  for 
relative  weights  is 

2H     +    0 

2  16 


H20 


1 8     Weight  proportions. 


And  for  the  volumetric  proportions: 


2H2    +    O2     =     2H20   (Steam). 


COMBUSTION  AND  HEAT  VALUES 


301 


The  weight  and  volume  proportions  of  the  gafces  involved  in 
the  combustion  of  hydrogen  in  air  are  given  in  the  following 
equation  for  one  pound  of  hydrogen. 


Cu.  ft. 


Pounds. 


455  Air- 

550  Products. 

360  N 

^6o~N 

190 

95 

190 

2H 

+    0 

H20 

[•' 

8 

9 

26.6  N 

26.6  N 

34.6  Air. 

35.6  Products 

And  for  one  cubic  foot  of  hydrogen : 


Cu.  ft. 


Pounds. 


2.39  Air. 

2.89  Products. 

1.89  N 

1.89  N 

I 

2H       + 

50 
0 

i.oo' 
H20 

^00528 

.04205 
.13968  N 

•0473 
.1397  N 

.17175  Air.     .1870  Products. 


206.  Economy  and  Efficiency  of  a  Combustion  Motor  as 
Affected  by  using  Calorimeter  Determinations  of  the  Heat  Value 
of  Hydrogen.  —  The  combustible  parts  of  the  fuels  used  in  com- 
bustion motors  are  hydrogen  and  carbon  with  possible  inappre- 
ciable amounts  of  other  chemical  elements.  The  carbon  of  the 
fuel  is  combined  with  either  oxygen  in  the  combustible  compound 
CO  or  with  hydrogen  in  some  of  the  numerous  hydrocarbons. 
Sometimes  more  than  half  of  the  volume  of  the  fuel  gas  is  free 
hydrogen,  as  in  some  of  the  water  gases. 

In  calorimeter  determinations  of  the  heat  value  of  fuels  the 
products  of  combustion  are  always  cooled  enough  to  condense 
the  steam  resulting  from  the  combination  of  H  with  O.  But  in 
the  case  of  the  internal-combustion  motor  the  H2O,  CO2,  and  N 
are  all  discharged  in  a  gaseous  state. 


302  THE   GAS  ENGINE 

The  fuel  economy  of  an  internal-combustion  motor,  or  any 
efficiency  that  involves  the  transformation  of  heat  energy  into 
mechanical  energy  when  using  fuel  mixtures  whose  combustible 
part  is  CO  only,  will  not  be  the  same  in  value  as  when  the  same 
motor  is  using  a  fuel  mixture  that  contains  H  if  the  heat  value 
of  the  H,  or  of  its  compounds,  is  based  on  calorimeter  determina- 
tions that  take  into  account  the  heat  given  up  by  the  condensation 
of  the  steam  produced  by  the  combustion  of  the  H,  when  all  other 
conditions  that  affect  the  thermal  efficiency  of  the  motor  are  the 
same  in  both  cases. 

The  extreme  differences  of  efficiencies  and  of  economies  will 
occur  when  the  combustible  part  of  the  fuel  in  one  case  is  CO 
only,  and  in  the  other  case  free  H  only.  While  the  combustible 
portions  of  the  fuels  that  are  used  in  combustion-motor  practice 
are  never  exclusively  CO  or  H,  the  assumption  that  a  motor 
operates  at  one  time  on  CO  as  the  sole  combustible,  and  at 
another  time  on  H  as  the  only  combustible,  gives  the  simplest 
means  of  showing  the  differences  of  fuel  economies  and  of  effi- 
ciencies, as  stated  above. 

It  will  also  be  assumed  that  a  given  motor  operates  under  a 
given  load  and  at  a  constant  speed.  The  indicated  horsepower 
of  the  impulses  (I.h.p.I)  must  then  always  be  the  same  without 
regard  to  the  kind  of  fuel  used,  if  the  mechanical  efficiency 
remains  constant.  Constant  mechanical  efficiency  will  be 
assumed. 

The  indicated  horsepower  of  the  impulses  (I.h.p.I)  of  a  given 
motor  at  constant  speed  is  directly  proportional  to  the  mean 
effective  pressure  of  the  impulse  (M.e.p.I).  The  M.e.p.I  must 
therefore  have  a  constant  value  for  a  constant  load. 

To  obtain  a  given  M.e.p.I  with  the  same  compression  pressure 
of  the  fuel  charge,  the  amount  of  heat  added  to  the  charge  by 
combustion  in  the  motor  must  be  the  same  in  all  cases,  whatever 
fuel  is  used,  provided  the  specific  heat  of  the  gases  in  the  cylinder 
after  combustion  is  the  same  whether  CO  or  H  is  the  combustible 
part  of  the  fuel  used.  Equal  specific  heats  will  be  assumed  for  the 
purpose  of  illustration. 

The  only  part  of  the  heat  of  combustion  of  H,  as  determined 


COMBUSTION  AND   HEAT  VALUES  303 

by  the  water-cooled  calorimeter  in  which  the  steam  of  combus- 
tion is  condensed,  that  is  effective  in  producing  temperature  and 
pressure  changes  in  the  steam,  is  that  in  excess  of  the  amount 
given  up  during  the  condensation  of  the  steam  produced  and  the 
cooling  of  the  watef  resulting  from  condensation.  This  may 
appear  clearer  by  following  the  application  of  heat  to  water 
to  convert  it  into  steam  and  then  to  superheat  the  steam  in  a 
closed  vessel  which  has  a  free-moving  piston.  The  first  part  of 
the  heat  raises  the  temperature  of  the  water  till  the  boiling  point 
is  reached.  Further  addition  of  heat  converts  the  water  into 
steam  without  increase  of  temperature,  the  pressure  remaining 
constant,  and  when  the  water  is  completely  evaporated  more 
heat  applied  goes  to  superheat  the  steam,  increasing  both  its 
temperature  and  volume  if  the  pressure  is  still  kept  constant  by 
the  movement  of  the  piston;  or,  if  the  piston  is  locked  in  position 
when  the  evaporation  is  complete,  the  temperature  and  pressure 
are  both  increased,  while  the  volume  remains  constant.  The 
steam  behaves  as  a  permanent  gas  as  long  as  the  temperature  is 
kept  somewhat  above  that  of  condensation  at  the  corresponding 
pressure.  The  only  part  of  the  heat  that  is  effective  in  raising 
the  temperature  and  pressure  of  the  steam  is  that  which  is  added 
after  the  water  is  completely  evaporated.  And,  conversely, 
when  the  steam  is  cooled,  the  heat  that  is  given  up  before  con- 
densation begins  represents  all  the  heat  that  is  useful  for  changing 
the  pressure,  volume,  and  temperature  of  the  steam.  The  same  is 
true  whenever  steam  gives  up  its  heat,  from  whatever  source  the 
heat  was  received. 

Each  pound  of  steam  formed  by  the  combustion  of  hydrogen 
gives  up  1146.6  B.t.u.  of  heat  when  it  is  condensed  from  212°  F. 
and  14.7  pounds  per  square  inch  absolute  pressure  and  the  water 
cooled  to  32°  F.  The  9  pounds  of  steam  formed  by  the  com- 
bustion of  one  pound  of  H  therefore  give  up,  during  the  same 
change, 

9  X  1146.6  =  10,320  B.t.u.  about. 

None  of  this  heat  (10,320  B.t.u.)  acts  on  the  gases  in  the  motor 
to  cause  changes  of  temperature  and  pressure,  for  the  tempera- 


304  THE   GAS  ENGINE 

ture  and  pressure  at  which  the  gases  are  discharged  from  the 
motor  are  higher  than  those  at  which  steam  condenses. 

The  total  heat  of  combustion  of  H,  as  determined  by  the  calo- 
rimeter, when  the  initial  temperature  of  the  combustible  mixture 
is  32°  F.  and  the  pressure  is  14.7  pounds  per  square  inch  absolute, 
and  the  resulting  products  cooled  to  the  same  temperature,  is 
about  62,100  B.t.u.  per  pound  of  H.  Of  this  there  are  10,320 
B.t.u.  that  have  no  effect  on  the  temperature  and  pressure  of  the 
steam  in  the  application  to  the  combustion  motor.  The 
remainder, 

62,100  -  10,320  =  51,780, 

is  all  that  is  effective  in  producing  changes  of  temperature  and 
pressure  in  the  gases  in  the  motor. 

Therefore  the  ratio  of  the  total  heat  of  combustion  of  H  (from 
32°  F.  and  14.7  pounds  per  square  inch  absolute  pressure  to 
water  at  the  same  temperature)  to  the  part  of  the  heat  that  is 
active  in  the  motor  is 

62,100 

=  1.2. 

5^780 

Under  the  assumptions  made,  if  100  B.t.u.  value  of  CO  is 
necessary  to  produce  the  required  mean  effective  pressure  of 
impulse  (M.e.p.I)  in  the  motor  when  CO  is  the  only  fuel,  then 
when  H  alone  is  used  as  the  fuel  120  B.t.u.  value  of  the  H  will 
be  required  to  obtain  the  same  M.e.p.I,  dealing  with  the  heat 
values  of  the  fuels  as  determined  by  the  calorimeter. 

The  ratio  of  the  thermal  efficiency  with  CO  to  that  with  H  as 
the  fuel  is  1.2  in  this  case.  The  ratios  of  the  total  efficiencies 
will  also  be  greater  than  unity.  The  economies  will  show  20  per 
cent  more  combustible  for  H  than  for  CO  when  expressed  in 
heating  values. 

In  making  a  guaranty  of  the  performance  of  a  motor,  expressed 
in  B.t.u.  per  delivered  horsepower,  or  in  efficiency,  it  would  there- 
fore be  necessary  to  know  the  composition  of  the  fuel  to  be  used 
if  the  calorimeter-determined  heat  values  are  to  be  -taken.  This 
would  bring  on  endless  difficulties.  In  order  to  avoid  such 


COMBUSTION  AND   HEAT  VALUES  305 

complications,  a  modification  of  the  heat  value  of  H,  or  of  any 
fuel  containing  H,  as  determined  by  the  water-cooled  calorimeter, 
has  been  brought  into  engineering  use.  This  modification  is 
known  as  the  " lower  heat  value"  of  the  fuel.  In  order  to  distin- 
guish between  the  calorimeter-determined  value  and  the  lower 
heat  value  the  former  is  called  the  "higher  heat  value." 

207.  Higher    Heat    Values.  —  Two    higher    heat    values    or 
calorific  powers  of  a  combustible  find  use  in  the  combined  fields 
of  engineering,  physics,  and  chemistry.     The  initial  temperature 
is  generally  taken   as  32°  F.   in   physics   and   chemistry.     The 
engineer  uses  a  higher  initial  and  final  temperature  in  order  to  be 
nearer  to  the  actual  conditions  of   practice.     This  higher   tem- 
perature will  be  taken  as  62°  F. 

The  heat  values  of  combustibles  that  do  not  contain  H  are  not 
appreciably  different  for  the  different  temperature  bases,  but 
there  is  a  marked  difference  when  H  is  present  in  considerable 
proportion. 

208.  Higher  Heat  Values  of  Hydrogen.  —  The  higher  heat 
value  of  H  from  32°  F.  and  14.7  pounds  per  square  inch  pressure 
to  water  at  the  same  temperature  and  pressure  has  already  been 
given  as  62,100  B.t.u.  per  pound. 

When  the  initial  temperature  of  the  combustible  mixture  is 
higher  than  32°  F.,  and  the  water  of  combustion  is  condensed  to 
the  same  (higher)  temperature,  there  will  be  a  modification  of 
the  higher  heat  value  just  given  on  account  of  the  difference  of  the 
specific  heats  of  the  combustible  mixture  and  of  the  water  formed. 
The  combustible  mixture  contains  more  heat  at  the  higher  tem- 
perature than  at  32°  F.,  and  this  additional  heat  is  a  gain  in  the 
heat  value.  But  the  condensed  water  also  has  more  heat  at 
the  higher  temperature  than  at  32°  F.,  and  this  causes  a  loss  in 
the  heat  value,  since  this  heat  is  retained  in  the  condensed  water 
and  not  given  up  to  the  calorimeter. 

For  illustrating  this,  the  specific  heats  of  the  substances  involved 
must  be  used. 

B.t.u. 

Specific  heat  of  H  per  pound  at  constant  pressure 3 .409 

Specific  heat  of  O  per  pound  at  constant  pressure 2I75 

Specific  heat  of  water  per  pound  can  be  taken  as  sufficiently 

accurate  for  this  purpose  at i  -  ooo 


306  THE  GAS  ENGINE 

For  an  initial  temperature  of  62°  F.  the  gain  of  heat  over  that 
at  32°  F.  for  1  pound  of  H  and  8  pounds  of  O  is: 

B.t.u. 

Gain  for  the  H  =  1  (62—32)  3.409  =   102.27 

Gain  for  the  O  =  8  (62—32)  2175= 52.20 

Total  heat  gain  for  9  pounds  combustible  =  .  .      154 

The  heat  deduction  for  the  final  temperature  (62°  F.)  of  the 
9  pounds  of  water  produced  is, 

B.t.u. 
Heat  loss  for  9  pounds  water  =  9  (62—32)  = 270 

Therefore  the 

B.t.u. 
Net  loss  =  270  —  154= 116 

and  the 

B.t.u. 
Higher  heat  value  of  H  per  pound  from  62°  F.  to 

62°  F.  water =62, 100  —  116= 61,984 

This  value  will  be  taken  as    62,000 

209.  Lower  Heat  Values.  —  The  lower  heat  value  of  H  is 
sometimes  assumed  as  the  amount  of  heat  that  would  be  given 
up  to  the  calorimeter  if  the  steam  product  of  combustion  were 
to  remain  gaseous  and  behave  in  the  same  manner  as  the  products 
of  combustion  of  the  other  chemical  elements  of  the  fuel  (and 
the  inert  nitrogen  when  the  O  for  combustion  is  supplied  by  air), 
instead  of  condensing  at  212°  F.  and  14.7  pounds  per  square  inch 
pressure. 

Under  this  assumption  the  lower  heat  value  is  less  than  the 
higher  by  an  amount  which  is  the  difference  between  (a)  the  heat 
given  up  by  the  steam  while  changing  from  steam  at  212°  F.  to 
water  at  whatever  final  temperature  is  taken  (below  212°  F.  and 
14.7  pounds  per  square  inch  pressure)  and  (b)  the  heat  that  would 
be  given  up  by  an  equal  weight  of  (imaginary)  gas  while  cooling 
from  212°  F.  to  the  same  assumed  final  temperature. 

The  amount  of  heat  given  up  by  a  pound  of  steam  in  condensing 
and  cooling  from  212°  F.  and  atmospheric  pressure  (14.7  pounds 
per  square  inch)  to  water  at  32°  F.  is  1146.6  B.t.u.  The  amount 


COMBUSTION  AND  HEAT  VALUES  307 

of  heat  that  would  be  given  up  by  a  pound  of  gas 'whose  specific 
heat  is  .24*  while  cooling  from  2i2°F.  to  32°  F.  (through 
i8o°F.)  is  180  X  .24  =  43.2  B.t.u.  The  difference  between 
the  heat  actually  given  up  by  the  pound  of  steam  and  that  given 
up  by  the  same  weight  of  the  imaginary  gas  is  1146.6  —  43.2  = 
1103.4  B.t.u.  One  pound  of  H  produces  9  pounds  of  steam. 
Therefore  the  difference  between  the  high  and  low  heat  values 
of  one  pound  of  H  when  the  products  of  combustion  are  cooled  to 
32°  F.  at  atmospheric  pressure  is 

9  X  1103.4  =  9930  B.t.u. 

When  the  pound  of  steam  is  condensed  from  2 1 2°  F.  and 
atmospheric  pressure  to  water  at  62°  F.,  it  gives  up  30  B.t.u. 
less  of  heat  than  when  it  is  cooled  to  water  at  32°  F.  The  amount 
of  heat  given  up  by  a  pound  of  steam  when  cooled  from  212°  F. 
and  atmospheric  pressure  to  water  at  62°  F.  is  therefore  1146.6  - 
30  =  1116.6  B.t.u.  One  pound  of  gas  with  a  specific  heat  of 
.24  (as  has  been  assumed)  gives  up  while  cooling  from  2i2°F. 
to  32°  F.  at  constant  pressure,  heat  to  the  amount  of 

1  (212  —  62)  .24  =  150  X  .24  =  36  B.t.u. 

The  difference  between  the  amount  of  heat  actually  given  up 
by  the  pound  of  steam  and  that  assumed  as  given  up  by  the  same 
weight  of  imaginary  gas  is  1116.6  —  36  =  1080.6  B.t.u.  There- 
fore the  difference  between  the  high  and  low  heat  values  of  one 
pound  of  H  when  the  initial  and  final  temperatures  are  62°  F. 
and  the  pressure  14.7  pounds  per  square  inch  is 

9  X  1080.6  =  9725  B.t.u. 

*  There  is  no  way  of  determining  what  the  specific  heat  of  this  imaginary 
gas  should  be.  Its  value  can  only  be  assumed  on  what  appears  to  be  a  reason- 
able basis.  The  specific  heat  per  pound  of  superheated  steam  increases 
rapidly  as  the  degree  of  superheat  increases.  If  the  specific  heat  of  the  imagi- 
nary gas  is  assumed  to  have  the  same  values  and  follow  the  same  law  down  to 
32°  F.,  its  mean  specific  heat  per  pound  would  be  in  the  neighborhood  of  .24 
probably.  If  the  imaginary  gas  were  taken  as  CO2  the  specific  heat  would 
be  about  .22  on  the  weight  basis.  Fortunately  only  a  very  small  relative  per- 
centage change  is  caused  in  determining  the  lower  heat  value  by  using  differ- 
ent values,  within  reasonable  limits,  of  this  assumed  specific  heat. 


308  THE  GAS  ENGINE 

The  amount  of  heat  deduction  per  pound  of  steam  (or  water) 
in  the  products  of  combustion  which  must  be  made  from  the 
higher  heat  value  to  obtain  the  lower  value,  appears  in  both  of 
the  above  cases.  It  is  shown  as  1103.4  B.t.u.  in  the  first  case  and 
as  1080.6  B.t.u.  in  the  second. 

In  applying  the  correction  to  the  calorimeter-determined  heat 
values  of  a  mixed  gas  to  obtain  its  lower  heat  value,  it  is  often 
convenient  to  use  the  correction  factor  for  each  pound  of  steam 
(or  water)  in  the  products  of  combustion.  The  values  just  given 
can  be  used  for  this  method  of  correcting,  each  in  its  proper 
place. 

A  summary  of  the  above,  together  with  the  lower  heat  values 
of  H,  under  the  two  conditions  stated,  is  given  below. 

Deduction  per  pound  of  H  to  be  made  from  the  higher  heat 
value  of  i  pound  of  H  to  obtain  the  lower  heat  value: 

B.t.u. 

For  initial  and  final  temperatures  of  32°  F 993° 

For  initial  and  final  temperatures  of  62°  F 97 2  5 

By  making  the  appropriate  deductions,  whose  values  have  just 
been  given,  from  the  higher  heat  values  of  H,  the  lower  heat  values 
are  obtained.  Thus : 

B.t.u. 

Lower  heat  value  of  one  pound  of  H  burned  from 
32°  F.  and  14.7  pounds  per  square  inch  and 
62°  F.  and  the  products  cooled  to  water  at 
32°  F.  is  62,100  —9930  = $2,17° 

Lower  heat  value  of  one  pound  of  H  burned  from 
62°  F.  and  14.7  pounds  per  square  inch  and 
the  products  cooled  to  water  at  62°  F.  is 
62,000-9725= 52,275 

Deduction  per  pound  of  steam  (or  water)  in  the  products  of 
combustion,  to  be  taken  from  the  higher  heat  value  of  a  fuel  to 
obtain  the  lower  heat  value: 

B.t.u. 

For  initial  and  final  temperatures  of  32°  F 1103 

For  initial  and  final  temperatures  of  62°  F 1080 


COMBUSTION  AND   HEAT  VALUES 


309 


Whenever  H,  either  free  or  combined,  is  prese/it  in  the  gas- 
motor  fuel  to  any  considerable  proportion  of  the  total  mixture  that 
enters  the  combustion  space  of  the  motor,  the  difference  between 
the  higher  and  the  lower  heat  values  of  the  fuel  is  great  enough  to 
need  consideration  in  accurate  economy  and  efficiency  determi- 
nations. 

TABLE    IV. 

Combustion  of  Carbon. 

Volumes  at  62°  F.  and  14.7  pounds  per  square  inch. 


Heat 
Value. 
B.t.u.    * 

Air  Required. 

Products. 

Lbs. 

Cu.  Ft. 

Lbs. 

Cu.  Ft. 

i  Ib  C  to  CO     .... 

4206 
14650 

5-76 
11.52 

75-8 
I5I-7 

6.76 
12.52 

91.7 
I5I-7 

i  Ib  C  to  CO2       

TABLE   V. 

Heat  Values  of  Gases. 

32°  Fahrenheit.     Pound  units. 


Gas. 

Air  per 
Lb.  of 

Perfect  Mix- 

tnt-0           "R    4-    11 

Product  per  Lb.  of 

Gas  for 

LuTC"      Jj.T.U. 

per  Lb. 

gas.      Lbs. 

B.t.u.  per  Lb. 

Perfect 

Chem- 

Mix- 

Name. 

ical 

ture. 

Form. 

Higher. 

Lower. 

Lbs.* 

Higher. 

Lower. 

C02 

H20 

N 

Hydrogen  

H2 

62,100 

^2,170 

34-6 

1744 

I46c 

9OO 
.  ww 

26.6 

Carbon  monox- 

3*>* /  w 

O    T 

•  /  T-T- 

J-tvO 

ide 

CO 

4,476 

4476 

2    4.6 

I2Q4 

I2Q4 

i   c;7 

i   80 

Methane      or 

T-JT-  /  " 

>T~  /  w 

•  •  T-W 

j.  -  ly-  1 

j.  -  '  ;-| 

L  •  j  / 

j.  .  t->y 

marsh  gas  .  .  . 

CH4 

23,850 

21,368 

17-3 

1303 

Il67 

2-75 

2.25 

13-3 

Ethylene  or  ole- 

fiant  gas  

C2H4 

2I,44O 

20,022 

14.83 

1354 

I26l 

3* 

If 

II.4 

Propylene  

C3H6 

21,420 

2O,O02 

14.83 

1353 

1262 

3* 

If 

il.  4 

Benzol  or  ben- 

zene vapor.  .  . 

•  C6H6 

l8,450 

17,686 

13-31 

I2QO 

I236 

3^ 

A 

10.25 

*  4.326  Ibs.  air  per  Ib.  of  Oxygen. 

Air  =  76.9%  H  and  23.1%  O  by  weight. 


3io 


THE   GAS  ENGINE 


TABLE    VI. 

Heat  Values  of  Gases. 

Cubic  foot  units  at  32°  F.  and  14.7  Ibs.  per  sq.  in.  pressure. 


Gas. 

Air  per 
Cu.  Ft.  of 
Gas  for 
Perfect 
Mixture. 
Cu.  Ft,* 

Perfect  Mix- 
ture. 
B.t.u.  per 
Cu.  Ft. 

Name. 

Chem- 
ical 
Form. 

B.t.u.  per 
Cu.  Ft. 

Higher. 

Lower. 

Higher. 

Lower. 

Hydrogen                

H2 
CO 
CH4 
C2H4 
C3H6 
C6H6 

348 

349 
1065 

1673 
2509 
4010 

292 
349 
955 
1562 

2343 
3845 

2-39 
2-39 
9-57 
14-35 
21.52 

35.87 

102.6 

103.0 
101  .4 
109.0 
111.4 
108.7 

86. 
103. 
90. 
101.7 
104.0 
104.3 

Carbon  monoxide      

Methane  or  marsh  gas 

Ethylene  or  olefiant  gas 

Propylene          

Benzol  or  benzene  vapor  

*  This  is  the  amount  of  air  required  for  a  perfect  mixture.     An  excess  of 
air  is  generally  used  in  practice. 

4.78  cu.  ft.  air  for  one  cu.  ft.  Oxygen. 


TABLE 

Heat  Values 

Cubic  Foot  units  at  62°  F.  and 


VII. 
of  Gases. 

14.7  Ibs.  per  sq.  in.  pressure, 


Gas. 

Perfect  Mix- 

Air per 

ture. 

Cu.  Ft.  of 

B.t.u.  per 

B.t.u. 

Gas  for 

Cu    Ft 

Na  TTIP 

Chemical 

per  Cu.  Ft. 

Perfect 
Mixture  j 

Form. 

Cu.  Ft. 

Higher. 

Lower. 

Higher. 

Lower. 

Hydrogen                 .        ... 

Ho 

328 

27<J 

2.  3Q 

06  6 

81 

Carbon  monoxide  

CO 

32Q 

32Q 

2  .  2O 

07-  o 

07. 

Methane  or  marsh  gas  

CH4 

1003 

9OO 

9-  57 

QC  .  C 

85. 

Ethylene  or  olefiant  gas 

C2H4 

1^77 

1472 

14.  1$ 

IO2     7 

06 

Propylene  

C3H6 

2364 

2205 

21.5* 

105.0 

98. 

Benzol  or  benzene  vapor  

C6H6 

3779 

3624 

35,-  87 

102.5 

98.3 

COMBUSTION  AND  HEAT  VALUES 


When  no  H  is  present  in  the  fuel,  there  is  only^one  heat  value 
for  the  fuel  between  any  stated  initial  and  final  temperatures. 
(This  of  course  does  not  refer  to  different  numerical  values 
expressed  in  different  units  of  measure.) 

Table  V  gives  the  heat  values  per  pound  at  32°  F.  and  14.7 
pounds  per  square  inch  pressure,  of  the  gases  with  which  com- 
bustion motors  are  most  concerned;  also  the  heat  values  of  a 
perfect  combustible  mixture  of  each  gas  with  air. 

Table  VI  gives  the  heat  value  of  gases  per  cubic  foot  at  32°  F. 
and  14.7  pounds  per  square  inch  pressure. 

Table  VII  gives  the  heat  values  of  gases  per  cubic  foot  at  62°  F. 
and  14.7  pounds  per  square  inch  pressure. 

TABLE   VIII.     PRODUCER    GAS  * 
Determination  of  Heat  Value  from  Chemical  Analysis. 

62°  F.  and  14.7  Ibs.  per  sq.  in  pressure. 


Components. 

Chemical 
Form. 

Percentage 
by  Volume. 

B.t.u.  per 
Cu.  Ft. 
Lower. 

B.t.u.  for 
Each  Com- 
ponent. 
Lower. 

P- 

h. 

pXh 

100 

Hydrogen 

H2 

Q.  7 

27<J 

26    67 

Carbon  monoxide 

CO 

16.4 

32Q 

C7     Q6 

Methane  

CH4 

<;.6 

QOO 

^O.4.O 

Carbon  dioxide 

CO2 

8    2 

Oxvcren 

C»9 

I    O 

Nitrogen 

N? 

CQ     I 

Total 

IOO.O 

131  .03 

*  Gas  made  in  a  pressure  producer  from  black  lignite  of  the  following 
percentage  composition  by  weight:  H  =  6.07;  C  =  57.46;  O  =  28.78;  N  =  1.15; 
S  =  .55;  Ash  =  5.99;  Total  =  100. 

Lower  heat  value  of  gas  at  62°  F.  and  14.7  Ibs.  per  sq.  in.  =  131 
B.t.u.  per  cu.  ft. 


312 


THE  GAS  ENGINE 


The  volumetric  composition  of  a  sample  of  producer  gas,  as 
determined  by  chemical  analysis,  is  given  in  Table  VIII ;  also  the 
tabulated  results  of  computations  for  the  lower  heat  value  of  the 
gas  per  cubic  foot  at  62°  F.  and  14.7  pounds  per  square  inch 
pressure. 

TABLE    IX.     PRODUCER    GAS. 

Density,  Air  Required,  and  Heat  Values  of  Gas  and  Mixture 
Determined  from  Chemical  Analysis. 

62°  F.  and  14.7  Ibs.  per  sq.  in.  pressure. 


"8 
?a 

•*  1 

^3 

|| 

aa 

J« 

*!« 

i?g 

Components. 

Chem- 
ical 
Form. 

Per  Cent  Volun 
Components. 

B.t.u.  perCu.  F 
Component.  ] 
Value. 

?  £ 

«   C 

if* 

Weight  of  Each 
ponent.  Lbs. 
Cu.  Ft.  of  Gas 

jii 

Air  for  Each  C 
ponent  in  a  Pe 
Mixture.  Cu. 

P- 

k. 

pxh 

P. 

pXD 

a. 

aXp 

IOO 

IOO 

IOO 

Hydrogen  

H2 
CO 

24.8 

275 
329 

23-37 
81.59 

.0736 

.00045 
.01825 

2-39 
2-39 

.203 
•593 

Carbon  monoxide  . 

Methane  

CH4 

S-2 

900 

46.80 

.0421 

.00219 

9-57 

.498 

Ethylene  

C2H4 

0.40 

1472 

5-89 

•0735 

.  00029 

M-35 

•057 

Carbon  dioxide.  .  .  . 
Oxvcren 

CO2 
02 

N2 

5-6 
0.40 

55-i 

.0841 
.0738 

.00647 
.00034 

•04055 

-4-873 

—  .019 

Nitrogen  .  . 

Totals  

1  00.0 

B.t.u.  =  157.  65 

Den,y=.c6854 

Air=  1.332 

B.t.u.  per  cubic  foot  of  gas  =  157.65  lower  value. 

Air  per  cubic  foot  of  gas  for  perfect  mixture  =  .332  cubic  foot. 

B.t.u.  per  cubic  foot  of  perfect  mixture  =    IM'  $    =67.5  lower  value. 

1  +  1.332 

Density  of  gas  =.0685  pound  per  cubic  foot  at  62°  F.  and  14.7 
pounds  per  square  inch. 

Table  IX  gives  the  volumetric  composition  of  another  sample 
of  producer  gas  together  with  the  computed  density,  air  required, 
and  lower  heat  values  of  the  gas  and  combustible  mixture. 


COMBUSTION  AND   HEAT  VALUES 


313 


Table  X  is  similar  to  Table  IX  for  an  illuminating  gas  made 
by  distilling  off  the  volatile  parts  of  the  coal  in  a  retort. 


TABLE    X.     RETORT   ILLUMINATING    GAS. 

Density,  Air  Required,  and  Heat  Values  of  Gas  and  Mixture. 
Determined  from  Chemical  Analysis. 

62°  F.  and  14.7  Ibs.  per  sq.  in.  pressure. 


| 

1% 

,     <u 

II 

|* 

Jlf. 

!!* 

p    o  *i 

||S 

0     4)        • 

o  4 

3  «• 

d  s 

JS 

%& 

^  ^  o 

|5^ 

Chem- 

> g 

G    0 

8.  o    . 

&3 

0 

"S 
*»  *> 

Jij 

Components. 

ical 

O       £ 

•  Is 

3    S  ~ 

•  +j 

•f  §s 

5  g  fe 

&"§ 

Form. 

g 

fll 

S     0    P 

•£?       ^        r- 

o3   •*"* 

n 

D     P,  O 

0. 

ffl 

« 

Q 

^ 

^ 

•^ 

pXh 

7) 

pxD 

aXp 

A 

100 

100 

IOO 

Hydrogen  

H2 

39-8 

275 

109.45 

•0053 

.002  i  i 

2-39 

•951 

Carbon  monoxide  . 

CO 

7.6 

329 

25.00 

.0736 

•00559 

2-39 

.184 

Methane  

CH4 

36.2 

900 

325.80 

.O42I 

.01524 

9-57 

3-464 

Propylene  *  

C3H6 

3-8 

22O5 

83-79 

.IIO4 

.00420 

21.52 

.818 

Benzol  f  

C6H6 

0.6 

3624 

21.74 

.2048 

.00123 

35-87 

.215 

Oxygen 

O2 

o  8 

O84I 

00068 

—  4    873 

—   038 

Nitrogen  

N2 

II.  2 

.0738 

.00827 

Totals  

100.  0 

B.t.u.= 

-565-78 

— 

,03^ 

Air 

=  5-594 

*  Heavy  hydrocarbons  taken  as  propylene. 
t  Light  hydrocarbons  taken  as  benzol. 

B.t.u.  per  cubic  foot  of  gas  =  565.78  lower  value. 

Air  per  cubic  foot  of  gas  for  perfect  mixture  =  5, 5 94  cubic  feet. 

B.t.u.  per  cubic  foot  of  perfect  mixture  =    •*  **'- —  =  85.8  lower  value. 

J  +  5-594 

Density  of  gas  =.0373  pound  per  cubic  foot  at  62°  F.  and   14.7 
pounds  per  square  inch. 


314  THE   GAS  ENGINE 

210.  Illuminants,  light  hydrocarbons  and  heavy  hydrocarbons. 

-  The  illuminating  property  of  a  gas  flame  depends  on  the 
presence  of  certain  hydrocarbons  known  as  the  "illuminants"  or 
" heavy  hydrocarbons."  In  their  absence  the  flame  has  little  or 
no  illuminating  power. 

In  gas  analysis  the  illuminating  hydrocarbons  are  not  generally 
separately  determined,  but  are  either  taken  as  a  single  group  or 
divided  into  two  groups  known  as  the  "light  hydrocarbons"  and 
the  "heavy  hydrocarbons."  These  light  hydrocarbons  are 
soluble  in  alcohol,  and  the  heavy  hydrocarbons  in  either  fuming 
sulphuric  acid  or  bromine. 

When  all  the  illuminants  are  determined  as  a  group,  they  are 
often  considered  as  propylene  (C3He).  When  divided  into  two 
groups,  the  light  hydrocarbons  may  be  taken  as  benzol  or  benzene 
(C6H6)  and  the  heavy  hydrocarbons  as  propylene. 

The  illuminants  are  also  sometimes  all  taken  as  ethylene 
(olefiant  gas,  C2H4). 

211.  Saturated  and  Unsaturated  Hydrocarbons.  —  The  hydro- 
carbons whose  chemical  compositions  agree  with  the  formula 
CnH2n+2,  of  which  CH4,  C2H6,  C3H8,  C4H10  are  examples,  are 
called  the  "paraffins."     They  are  also  called  "saturated  hydro- 
carbons."    The  carbon  in  them  is  completely  saturated  with 
hydrogen,  or  at  least  more  completely  saturated  than  any  of  the 
other  known  hydrocarbons. 

The  other  hydrocarbons  with  which  the  combustion  motor 
and  gas  manufacture  for  it  are  concerned,  are  called  the  "un- 
saturated  hydrocarbons."  They  are  the  illuminants  mentioned 
in  the  preceding  section.  They  conform  to  various  chemical 
formulas,  some  of  which  are  given  below. 

The  olefine  group  has  the  formula  CnH2n.  Some  of  the  com- 
pounds are  C2H4,  C3H6,  C4H8. 

The  acetylene  group  has  the  formula  CnH2n_2.  Acetylene  gas 
has  the  composition  C2H2. 

The  benzols  or  benzenes  (not  the  benzine  from  petroleum)  are 
represented  by  the  general  formula  CnH2n_c.  Of  them  benzene, 
C6H6,  is  found  in  coal  gas. 

Naphthalene,  of  another  group,  has  the  composition  C10H8. 


COMBUSTION  AND   HEAT  VALUES  315 

The  tar  of  coal  gas  is  composed  of  naphthalene  jand  other  com- 
pounds of  a  similar  nature. 

212.  Physical  Form  of  Hydrocarbons.  —  At  or  near  atmos- 
pheric pressure  the  hydrocarbons  with  which  this  work  is  most 
concerned  have  the  following  conditions  as  to  being  gas,  liquid,  or 
solid. 

Methane  (marsh  gas,  CH ),  ethylene  (olefiant  gas,  C2H4), 
propylene,  C3He,  ethane,  C2H6,  and  acetylene,  C2H2,  all  are  per- 
manent gases  at  atmospheric  temperatures. 

Propane,  C3H8,  is  a  gas  above  1.4°  F. 

Butane,  C4H10,  is  a  gas  above  34°  F. 

Benzole  or  benzene,  C6H6  (not  the  benzine  from  petroleum, 
or  the  refined  benzol  which  is  used  in  the  same  manner  as 
gasoline  in  combustion  motors),  melts  at  42°  F.  and  boils  at 
177°  F.,  above  which  temperature  it  is-  a  gas.  Refined  benzol 
freezes  at  about  —  20°  F. 

Naphthalene,  C10H8,  melts  at  175°  F.  and  boils  at  424°  F. 

The  vapors  of  substances  present  but  not  gaseous  under  the 
conditions  existing  are  generally  present  in  the  gas  with  which 
the  substance  is,  or  has  been,  in  contact.  This  is  similar  to  the 
presence  of  water  vapor  in  air  at  atmospheric  temperatures. 

213.  Dissociation  or  Decomposition  of  Chemical  Compounds. 
-  Experiments  have  shown  that  if  steam  is  heated  to  a  high 

temperature  part  of  it  is  separated  into  its  elements  H  and  O. 
The  proportion  of  the  whole  mass  that  is  dissociated  or  "  split 
up"  is  greater  the  higher  the  temperature.  As  far  as  has  been 
determined  and  made  public,  the  temperature  at  which  dissocia- 
tion of  H2O  begins  is  in  the  neighborhood  of  1800°  F.  When  the 
temperature  is  lowered  again,  the  elements  H  and  O  recombine 
if  they  have  not  been  acted  on  by  other  chemical  elements. 

Several  of  the  chemical  compounds  of  hydrogen  and  carbon 
(hydrocarbons)  that  are  contained  in  petroleum  and  its  distillates 
(kerosene,  naphtha,  gasoline,  etc.)  and  in  bituminous  coals,  are 
decomposed  or  split  up  when  heated  to  a  temperature  far  lower 
than  that  of  combustion  of  the  liquid  or  coal.  The  elements  of 
the  hydrocarbons  thus  separated  generally  unite  immediately  in 
different  proportions  from  those  in  which  they  were  combined 


316  THE  GAS  ENGINE 

before  heating,  and  thus  form  new  hydrocarbons  whose  physical 
and  chemical  properties  are  unlike  those  of  the  original  compound. 

Dissociation  is  the  reverse  of  chemical  combination,  and  the 
heat  required  to  cause  the  dissociation  is  the  same  in  amount  as 
that  which  was  liberated  during  the  combination  of  the  same 
amount  of  elements  to  form  the  chemical  compound. 

214.  Combustion  Pressures  and  Temperatures.  —  If  the  specific 
heats  of  gases,  or  the  total  amount  of  heat  in  the  gases,  were 
known  for  all  temperatures  between  those  of  combustion  and 
atmospheric,  then  the  theoretical  temperature  of  the  products  of 
combustion  could  be  readily  calculated.  These  heat  properties 
of  the  gases  are  not  known,  however,  for  the  high  temperatures 
of  combustion.*  It  is  therefore  impossible  to  calculate  even 
approximately  on  this  basis  the  pressure  that  a  combustible 
mixture  will  produce  when  burned  either  in  a  vessel  of  fixed 
volume  or  in  one  of  variable  volume,  or  otherwise. 

The  cooling  effect  of  the  walls  of  the  cylinder  or  vessel  in  which 
the  gas  is  contained  has  much  to  do  with  lowering  the  pressure 
below  that  which  would  be  attained  if  there  were  interchange  of 
heat  between  the  gas  and  the  walls.  The  walls  of  a  metal  vessel 
abstract  heat  with  great  rapidity  from  gases  at  as  high  tem- 
peratures as  those  produced  by  the  combustion  of  the  fuels 
used  in  gas-engine  practice,  when  the  walls  are  kept  as  cool  as 
they  must  be  in  the  motor. 

Investigations  by  different  experimenters  with  combustible 
mixtures  of  illuminating  gas  and  air,  exploded  at  atmospheric 
pressure  in  cast-iron  cylinders  some  •  7  or  8  inches  in  diameter 
and  somewhat  longer  than  the  diameter,  show,  for  proportions 
of  air  and  gas  giving  the  higher  pressures,  that  the  pressure  drops 

*  Recent  investigations  show  that  the  specific  heats  of  CO,  CO2,  and  steam 
all  increase  with  rise  of  temperature.  The  results  obtained  by  different 
experimenters  for  CO  and  CO2  are  so  far  different  at  the  higher  temperatures 
as  to  make  it  impossible  to  select  approximately  correct  values.  The  specific 
heat  of  steam  has  been  determined  by  Prof.  C.  C.  Thomas  for  temperatures 
up  to  something  more  than  850°  F.  and  300  pounds  per  square  inch  pressure. 
(Proceedings  Amer.  Soc.  Mech.  Engrs.,  December,  1907.)  Neither  this  tem- 
perature nor  pressure  is  as  high  as  in  the  combustion  motor.  The  tem- 
perature especially  is  far  below  that  of  combustion  in  the  motor. 


COMBUSTION  AND  HEAT  VALUES  317 

from  the  maximum  to  about  half  the  maximum  jn  one-fourth  of 
a  second  or  less,  and  during  a  full  second  falls  to  about  one-fifth 
of  the  maximum,  but  as  low  as  one-seventh  of  the  maximum  in 
some  cases.  The  maximum  pressures  of  the  mixtures  giving 
the  higher  values  are  attained  in  one-fifteenth  to  one-twentieth  of 
a  second,  as  indicated  by  the  recording  apparatus.  These 
values  make  no  allowance  for  the  inertia  lag  of  the  moving  parts 
of  the  indicator. 

With  the  higher  temperatures  and  pressures  that  occur  in  the 
combustion  motor  on  account  of  compression  before  ignition,  the 
rate  of  heat  absorption  by  the  cylinder  walls  is  much  more  rapid 
during  the  early  part  of  the  stroke  than  later  in  the  stroke, 
except  possibly  in  the  case  of  a  very  hot  motor  cylinder. 

215.  Rate  of  Flame  Propagation  and  Combustion.  —  When 
a  quiescent  mass  of  combustible  gas  and  air  mixture  is  ignited  by 
a  spark,  the  flame  propagates  itself  through  the  mixture  by 
spreading  in  a  spherical  wave,  at  least  theoretically.  The  actual 
propagation  is  something  of  this  nature,  at  least.  An  appreciable 
period  of  time  in  comparison  with  that  required  for  one  stroke 
of  the  piston  of  a  high-speed  motor  is  required  for  the  flame  to 
pass  through  the  entire  mass.  The  location  of  the  igniting  spark 
in  the  mass  of  mixture  therefore  has  to  do  with  the  time  required 
for  complete  inflammation  of  the  charge.  If  the  spark  occurs  in 
a  pocket  leading  off  from  the  main  combustion  chamber,  as  is  the 
case  in  many  gas  motors,  the  charge  will  not  be  inflamed  as 
quickly  as  if  the  spark  were  in  the  center  of  the  combustion 
chamber.  Again,  if  there  is  a  pocket  on  each  side  of  the  com- 
bustion chamber,  the  inflammation  will  be  completed  sooner  by 
making  simultaneous  sparks  in  the  two  pockets  than  by  igniting 
in  only  one  pocket.  With  the  two  sparks  the  flame  has  only 
about  half  as  far  to  travel  as  with  the  one. 

When  the  initial  ignition  of  the  charge  is  in  a  relatively  small 
reservoir  connected  to  the  main  mass  of  the  gas  by  a  narrow 
passage,  a  jet  of  flame  is  projected  into  the  main  body  of  the  gas 
and  ignites  a  large  portion  quickly.  The  indicator  card  in  such 
a  case  shows  a  rapidly  rising  combustion  line  without  any  sign  of 
ignition  before  the  completion  of  the  compression  stroke.  The 


318  THE   GAS  ENGINE 

ignition  must  be  somewhat  before  the  completion  of  compression, 
however,  in  order  to  have  the  flame  project  into  the  main  mass 
before  the  piston  has  moved  appreciably  on  the  impulse  stroke. 

After  inflammation,  some  time  is  required  for  the  completion 
of  combustion.  This  is  plainly  noticeable  in  the  burning  of  a 
candle  or  a  Bunsen  flame.  In  the  flame  the  period  of  uniting  is 
that  during  which  the  atoms  travel  from  the  bottom  to  the  top 
of  the  flame. 

The  rate  of  combustion  is  affected  by  variation  of  pressure  and 
of  the  proportions  of  the  air  and  fuel  within  the  range  of  com- 
bustible mixtures.  It  is  probable  that  the  rate  of  combustion 
also  varies  with  the  temperature,  but  this  has  not  been  conclu- 
sively proved. 

The  combustion  is  more  rapid  the  higher  the  pressure  of  the 
mixture. 

A  perfect  mixture  burns  more  rapidly  than  one  that  is  "lean" 
or  too  "rich."  A  theoretically  perfect  mixture  is  one  in  which 
there  is  just  enough  oxygen  present  to  unite  with  the  fuel  in  the 
proportion  to  form  the  most  stable  compound.  A  practically 
perfect  mixture  contains  a  slight  excess  of  oxygen  above  the 
amount  for  a  theoretically  perfect  mixture.  A  lean  mixture  has 
too  little  fuel  and  more  oxygen  than  is  necessary  for  complete 
combustion.  The  same  name  is  also  applied  to  a  mixture  having 
the  proper  proportions  of  fuel  and  oxygen  but  which  is  diluted 
with  inert  gases  such  as  those  remaining  in  the  combustion 
chamber  of  a  motor  and  mixing  with  the  next  charge.  A  rich 
mixture  has  more  fuel  than  is  necessary  for  the  proper  propor- 
tion relative  to  the  oxygen  present  for  complete  combustion. 

The  "time  of  combustion"  as  herein  used  means  the  interval 
between  the  ignition  of  the  first  part  of  the  mixture  and  the 
ceasing  of  combustion.  It  includes  ignition,  inflammation,  and 
combustion,  more  or  less  chemically  complete,  as  the  case  may  be. 

216.  Unusual  Pressures  of  Combustion.  —  Under  certain 
conditions  the  pressure  produced  by  the  combustion  of  a  gas 
and  air  mixture  is  higher  than  those  ordinarily  occurring.  The 
conditions  conducive  to  such  unusual  pressure,  so"  far  as  they 
seem  to  have  been  determined,  are  those  in  which  the  combustion 


COMBUSTION  AND   HEAT  VALUES  319 

of  one  portion  of  a  mass  of  gas  produces  high  pressure  in  an 
unignited  portion,  and  the  latter  then  appears  to  suddenly  ignite 
and  burn  with  a  resulting  high  pressure. 

The  effect  of  pockets  and  contracted  ducts  has  already  been 
mentioned  in  connection  with  indicator  cards.  In  this  relation 
it  may  be  pointed  out  that  the  cooling  action  of  a  small  contracted 
duct  may  prevent  the  passage  of  the  propagating  flame  into  a 
pocket  thus  partly  cut  off  from  the  main  body  of  the  gas  till  the 
pressure  has  become  so  high  that  the  mixture  in  the  pocket 
explodes  violently. 

There  seem  to  be  no  conclusive  proofs  of  the  infrequent  occur- 
rence of  combustion  pressures  enormously  higher  than  the  usual 
values  in  gas-engine  practice.  For  many  years  it  was  supposed 
that  these  pressures  did  occur  in  the  motor  and  were  the  chief 
cause  of  broken  parts,  especially  the  cylinder.  The  writer  has 
searched  for  but  never  been  able  to  find  such  a  case.  Internal 
stresses  due  to  heating  seem  to  be  more  accountable  for  breakages 
of  this  nature. 

217.  When  an  over-rich  mixture  of  air  and  gasoline  vapor  is 
ignited,  all,  or  nearly  all,  of  the  hydrogen  (of  the  hydrocarbons 
of  which  the  gasoline  is  composed)  unites  with  the  oxygen  present, 
thus  not  leaving  a  sufficient  amount  of  O  for  all  the  carbon  to 
unite  with.  The  carbon  thus  left  appears  as  soot  or  smoke  which, 
in  the  case  of  a  combustion  motor,  is  discharged  with  the  exhaust 
gases,  except  such  of  it  as  adheres  to  the  walls  of  the  combustion 
chamber,  ports,  and  other  parts  with  which  it  comes  in  contact. 

The  imperfect  combustion  is  responsible  for  a  loss  of  heat  both 
on  account  of  the  heat  required  for  dissociating  the  hydrocarbon, 
part  of  which  is  not  burned,  and  on  account  of  the  failure  of  the 
carbon  to  burn. 

In  the  case  of  gaseous  fuels,  smoke  may  or  may  not  appear, 
according  to  the  nature  of  the  fuel,  but  in  all  cases  the  imperfect 
combustion  of  course  means  loss  of  heat.  A  gas  rich  in  illumi- 
nants  will  give  off  smoke  when  the  mixture  is  too  rich. 

Producer  gas  from  bituminous  coals  is  generally  richer  and 
contains  a  greater  proportion  of  illuminants  just  after  a  fresh  lot 
of  fuel  has  been  charged  on  than  after  there  has  been  no  fresh 


320  THE   GAS   ENGINE 

fuel  added  for  some  time.  This  is  on  account  of  the  distillation 
of  the  volatile  part  of  the  fresh  fuel  soon  after  it  is  put  into  the 
producer. 

218.  Moisture  in  Air  and  Gas.  —  The  moisture  in  air  and  gas 
exists  in  the  state  of  vapor  when  the  quantity  does  not  exceed  the 
limit  that  the  air  or  gas  will  take  up  as  vapor.  When  this  limit 
is  reached,  the  air  or  gas  is  said  to  be  saturated  with  water  vapor. 

In  the  case  of  fog  in  air  (or  gas)  there  is  present  more  than 
enough  moisture  to  produce  saturation,  and  the  excess  is  in  the 
form  of  finely  divided  (atomized,  in  popular  language)  liquid 
water.  The  same  is  true  when  dew  is  falling.  This  atomized 
water  may  be  called  entrained  water. 

The  weight  of  the  water  whose  vapor  will  just  saturate  a  given 
volume  of  space  varies  with  the  tempera ture,_  but  is  not  changed 
by  change  of  pressure  or  of  the  kind  of  gas  present.  The  weight 
of  water  vapor  for  just  saturating  a  cubic  foot  of  space  at  a  given 
temperature  is  the  same  whether  the  space  contains  air  or  gas,  or 
is  a  vacuum  before  the  water  vapor  is  added.  If  liquid  water  is 
flowed  into  the  vacuum  it  will  vaporize  very  much  more  quickly 
to  saturate  the  space  than  if  the  "space"  is  filled  with  dry  air  or 
dry  gas  at  atmospheric  pressure  before  the  water  is  flowed  in; 
but  the  weight  of  the  water  that  will  finally  vaporize  is  the  same 
in  either  case.  As  a  concrete  example,  if  something  more  than 
14.79  grains  of  water  are  added  to  dry  air,  dry  gas,  or  a  vacuum 
of  one  cubic  foot  enclosed  volume,  the  space  will  be  saturated  at 
90°  F.  by  the  vaporization  of  14.79  grains  of  the  water.  The 
water  in  excess  of  this  amount  will  remain  liquid. 

The  water  vapor  in  a  saturated  space  has  an  invariable  pressure 
for  each  temperature.  The  pressure  of  the  water  vapor  is  not 
changed  by  the  presence  or  absence  of  air,  gas,  or  other  vapors. 
When  the  water  vaporizes  in  the  enclosed  dry  space,  the  pressure 
against  the  enclosing  walls  is  increased  by  the  amount  of  the 
vapor  pressure  for  the  corresponding  temperature.  The  vapor 
pressure  for  saturation  at  90  degrees  is  .691  pound  per  square 
inch.  The  pressure  against  the  enclosing  walls  will  be  increased 
by  this  amount  on  account  of  the  vaporization  of  the  water.  If 
the  cubic  foot  of  space  is  originally  filled  with  dry  air  or  dry  gas 


COMBUSTION  AND  HEAT  VALUES  321 

at  14  pounds  per  square  inch  pressure,  it  will  have,  when  saturated 
with  water  vapor,  a  pressure  of  14  +  .691  =  14.691  pounds  per 
square  inch  at  90°  F. 

The  relative  volumes  occupied  by  the  dry  air  and  water  vapor 
are  proportional  to  their  individual  pressures.  At  90°  F.  the  ratio 
of  the  volume  of  the  water  vapor  to  that  of  the  dry  air  is  .691  to 
14,  which  corresponds  to  4.7  per  cent  water  vapor  and  95.3  per 
cent  dry  air. 

Table  XI  gives  data  of  the  above  nature  for  different  tem- 
peratures. The  table  shows  that  the  proportion  of  water  vapor 
increases  rapidly  with  increase  of  temperature. 

If  the  vapor  pressure  is  kept  constant  at  (or  below)  the  satura- 
tion pressure,  all  of  the  liquid  will  vaporize.  Heat  must  be 
added  to  keep  the  temperature  constant.  Water  boiling  in  the 
open  air  is  an  example  of  this.  In  an  enclosed  space  with  an 
opening  for  allowing  the  vapor  to  escape,  the  vapor  or  steam  thus 
ultimately  occupies  the  entire  volume  of  the  space. 

The  extent  of  the  effect  of  variation  of  moisture  on  the  working 
of  a  combustion  motor  can  be  seen  by  the  aid  of  a  concrete  case. 
A  motor  operating  on  gasoline  is  convenient  to  deal  with.  It  will 
be  assumed  that  when  the  inlet  closes  the  charge  has  the  same 
temperature  in  the  motor  as  the  air  outside. 

At  92°  F.  and  100  per  cent  humidity  (complete  saturation), 
the  moist  air  will  be  95  per  cent  dry  air  and  5  per  cent  water  vapor 
by  volume.  At  92°  F.  and  50  per  cent  humidity  (half  saturation) 
the  volume  of  the  vapor  will  be  only  half  as  great,  as  will  be  the 
vapor  pressure  and  weight  of  vapor  per  cubic  foot.  The  air  at 
90  degrees  and  50  per  cent  humidity  will  therefore  be  97.5  per 
cent  dry  air  and  2.5  per  cent  water  vapor.  This  is  an  increase  of 
about  2.6  per  cent  in  the  volume  of  dry  air.  The  oxygen  for 
supporting  combustion  is  increased  in  the  same  proportion. 
The  motor  will  therefore  develop  more  power  on  the  dry  air  than 
on  the  saturated.  A  range  of  humidity  as  great  as  that  stated, 
or  even  greater,  is  not  unusual,  and  fog  gives  greater  moisture 
than  100  per  cent  humidity. 

The  cooling  'of  air  or  gas  precipitates  moisture  if  present  in 
sufficient  quantity,  as  in  the  familiar  example  of  dew. 


322 


THE  GAS  ENGINE 


TABLE   XI.* 

Moisture  in  Air,  Gas,  or  Vacuum   Completely  Saturated  With 
Water  Vapor  at  Different  Temperatures. 

Complete  saturation  corresponds  to  100  per  cent  humidity. 


Temperature. 

Vapor  Pressure. 

Percentage  by  Volume 
in  a  Saturated  Mix- 
ture at  14.7  Lbs. 

Weight  of  Water 
Vapor  per  Cubic 
Foot 

per  Sq.  In. 

Deg. 

Fahr. 

Deg. 
Cent. 

Inches  of 
Mercury. 

Pounds 
per 
Sq.  In. 

Water 
Vapor. 

Dry  Gas. 

Grains. 

Pounds  . 

—  20 

-28.9 

.0126 

.0062 

.04 

99.96 

.166 

.  000024 

—  10 

-23-3 

.0222 

.0109 

.07 

99-93 

.285 

.000041 

o 

-I7.8 

•0383 

.0188 

•13 

99.87 

.481 

.000069 

5 

-15 

.0491 

.0241 

.16 

99.84 

.610 

.000087 

IO 

—  12.2 

.0631 

.0310 

.21 

99-79 

.776 

.0001  I  i 

15 

-  9-4 

.0810 

.0398 

.27 

99-73 

.986 

.000141 

20 

-   6.7 

.  1026 

.0504 

•34 

99.66 

l-235 

.000176 

25 

-   3-9 

.130 

.0639 

•43 

99-57 

J-SS1 

.000221 

30 

—    i.i 

.164 

.0806 

•55 

99-45 

J-935 

.000276 

32 

0 

.180 

.0884 

.60 

99.40 

2.113 

.  OO0302 

35 

i-7 

.203 

.099 

.62 

99-38 

2.366 

•  000338 

40 

4-4 

•247 

.  121 

.82 

99.28 

2.849 

.  O00407 

45 

7.2 

.298 

.146 

•99 

99.01 

3-414 

.  000488 

5° 

10.  0 

.360 

.177 

.20 

98.80 

4.076 

.000582 

52 

ii  .  i 

.387 

.  I9O 

.29 

98.71 

4-372 

.000625 

54 

12.2 

.417 

.205 

.40 

98.60 

4.685 

.  000669 

56 

13-3 

.448 

.220 

•5° 

98.50 

5.016 

.000717 

58 

14.4 

.482 

•236 

.61 

98.39 

5-37o 

.000767 

60 

I5.6 

•5i7 

•254 

•73 

98.27 

5-745 

.  00082  I 

62 

l6-7 

•555 

•273 

.86 

98.14 

6.  142 

.000877 

64 

I7.8 

•595 

.292 

•99 

98.01 

6-563 

.  000938 

66 

18.9 

.638 

•314 

2.14 

97.86 

7.009 

.OOIOOI 

68 

20.0 

.684 

•336 

2.28 

97.72 

7.480 

.001069 

70 

21  .  I 

•732 

•359 

2.44 

97-56 

7.980 

.001140 

*  Inches  of  mercury  for  vapor  pressure  and  grains  weight  of  water  vapor 
taken  from  Psychrometric  Tables  of  the  United  States  Weather  Bureau. 
Other  items  computed  by  the  author. 


COMBUSTION  AND  HEAT  VALUES 


323 


TABLE  XI.*— CONTINUED. 

Moisture  in  Air,  Gas,  or  Vacuum  Completely  Saturated  With 
Water  Vapor  at  Different  Temperatures. 

Complete  saturation  corresponds  to  100  per  cent  humidity. 


Temperature. 

Vapor  Pressure. 

Percentage  by  Volume 
in  a  Saturated  Mix- 
ture at  14.7  Lbs. 
per  Sq.  In.- 

Weight  of  Water 
Vapor  per  Cubic 
Foot. 

Deg. 
Fahr. 

Deg. 
Cent. 

Inches  of 
Mercury. 

Pounds 
per 
Sq.  In. 

Water 
Vapor. 

Dry  Gas. 

Grains. 

Pounds. 

72 
74 
76 

22.2 

23-3 
24.4 

.783 
.838 
.896 

.384 
.412 
.440 

2.61 

2-79 
2.99 

97-39 
97.21 
97.01 

8.508 
9.066 
9.655 

.001215 
.001295 
.001379 

g 

82 

25.6 
26.7 

27.8 

•957 
i.  022 
1.091 

•  47° 
.502 

.536 

3-20 

3-42 
3-65 

96.80 
96.58 
96.35 

10.277 
10.934 
II  .626 

.001468 
.001562 
.001661 

84 
86 

88 

28.9 
30.0 
31-1 

1.163 
1.241 
1.322 

.p 
.610 
.650 

3-89 
4.15 
4.42 

96.  II 
95-85 
95-58 

12.356 
13.127 

13-937 

.001765 
.001875 
.001991 

90 
92 
94 

32.2 

33-3 

34.4 

1.408 
1.499 
1-595 

.691 
.736 
.784 

4.70 
5.00 
5-33 

95-3° 
95.00 
94.67 

14.790 
15-689 
16.634 

.002113 
.002241 
.002376 

96 
98 

IOO 

35.6 

36-7 
37-8 

1.696 
1.803 
1.916 

•833 
.887 
.942 

5.67 

6.03 

6.41 

94-33 
93-97 
93-59 

17.  626 
18.671 
19.  766 

.002518 
.002667 
.002824 

102 
104 

106 

38.9 
40.0 
41.1 

2-035 
2.160 
2.292 

I.  00 

1.061 
1.126 

6.81 

7%22 

7.67 

93-19 
92.72 

92.33 

20.917 

22.  125 
23.392 

.  002988 
.003161 
.00334! 

108 
no 

210 

42.2 
43-3 

08.  Q 

2-431 
2.576 

28.7=; 

1.194 
i.  264 

14.  II 

8.12 

8.60 

06.00 

91-87 
91.40 

4.00 

24.720 
26.  112 

•003531 
.003730 

*  Inches  of  mercury  for  vapor  pressure  and  grains  weight  of  water  vapor 
taken  from  Psychrometric  Tables  of  the  United  States  Weather  Bureau. 
Other  items  computed  by  the  author. 


324  THE  GAS  ENGINE 

A  cubic  foot  of  saturated  air  at  32°  F.  contains  but  13.5  per 
cent  as  much  moisture  by  weight  as  a  cubic  foot  at  92°  F.  and  the 
volume  occupied  by  the  vapor  is  but  12  per  cent  of  that  at  92°  F. 
A  cubic  foot  of  saturated  air  at  92°  F.  when  cooled  to  32  degrees 
contains  only  11.5  per  cent  as  much  water  vapor  by  weight  as 
at  92°  F. 

Compressing  saturated  air  or  gas  at  constant  temperature 
reduces  the  weight  of  water  vapor  in  it  by  condensation.  For 
the  vapor  pressure  remains  constant  and  the  weight  of  vapor  in 
the  reduced  space  is  proportional  to  the  volume  of  the  space; 
but  compressing  air  or  permanent  gas  does  not  decrease  its 
weight,  therefore  the  weight  proportion  of  water  vapor  is  decreased 
by  compression. 

Sudden  expansion  of  saturated  compressed  air  or  gas  cools  it 
so  that  some  of  the  water  vapor  is  condensed  and  may  be  pre- 
cipitated. 

Producer  gas  is,  on  account  of  cooling  while  being  washed  with 
water,  saturated  with  water  vapor  when  it  leaves  the  scrubber. 
It  may  also  carry  entrained  liquid  water.  In  warm  weather  the 
amount  of  moisture  may  be  enough  to  affect  the  power  of  the 
motor  sufficiently  to  deserve  attention. 

Saturated  gas  at  92°  F.  and  14.7  pounds  per  square  inch  has 
only  95  per  cent  of  the  heating  capacity  of  dry  gas  at  the  same 
temperature  and  pressure,  dealing  with  volumes. 

A  saturated  combustible  mixture  at  92°  F.  and  14.7  pounds 
per  square  inch  also  has  95  per  cent  of  the  heating  value  per  cubic 
foot  that  the  dry  mixture  has.  The  pressure  of  combustion  is 
reduced  by  the  water  vapor  both  on  'account  of  the  reduction  of 
the  heat  value  and  the  higher  specific  heat  of  water  vapor  or  steam. 
Water  in  suspension  requires  heat  to  vaporize  it,  which  is  lost  in 
gas-engine  practice. 

The  moisture  can  be  largely  removed  by  compressing  and 
cooling  the  gas  and  then  allowing  it  to  expand  suddenly.  Cen- 
trifugal motion  after  compression  will  remove  water  of  conden- 
sation. 

219.  Gas  Analyses  Relative  to  Moisture.  —  Published  reports 
of  gas  analyses  seldom  make  any  statement  regarding  moisture. 


COMBUSTION  AND  HEAT  VALUES  325 

Computed  heat  values  based  on  chemical  analyse*  which  do  not 
take  moisture  into  account  give  higher  heat  values  for  the  gas 
than  the  actual  values. 

Humidity  of  gas,  or  moisture  not  exceeding  the  saturation 
point,  can  be  determined  by  the  wet-  and  dry-bulb  thermometer 
apparatus  in  common  use  by  the  Weather  Bureau.  Entrained 
moisture  can  be  measured  by  absorption  methods. 


CHAPTER  XVIII. 


FUELS   AND  GAS    MAKING. 

220.  General.  —  The  commercial  form  in  which  fuel  is 
obtainable,  its  cost,  and  the  convenience  with  which  it  can  be 
used  in  the  internal-combustion  motor  are  the  chief  items  in  the 
consideration  of  the  selection  of  the  type  of  motor  and  in  deter- 
mining the  kind  of  fuel. 

The  fuels  either  found  on  the  market  or  resulting  as  by-products 
of  industrial  processes,  with  which  the  combustion  motor  is 
mostly  concerned,  and  the  general  methods  of  utilizing  them,  are : 


Coal. 

Lignite. 

Peat. 

Wood. 

Charcoal 

Crude  petroleum. 
Heavy  distillates  of 
petroleum. 

Kerosene. 

Naphtha. 
Gasoline. 
Alcohol. 
Benzol. 

Natural  gas. 
Illuminating  gas. 
Fuel  gas. 
Blast-furnace  gas. 
Coke-oven  gas. 


Converted  into  gas  in  a  gas  producer 
before  using.  Washing  and  puri- 
fying the  gas  are  generally  advis- 
able. 

Injected  into  the  motor  cylinder  or 
transformed  into  permanent  gas 
by  the  application  of  heat. 

/Injected  into  the  motor  cylinder  or 
I     vaporized  in  a  heated  carbureter. 


Vaporized  in  a  carbureter. 


Used  as  received,  except  that  clean- 
ing or  washing  is  necessary  for 
the  by-product  gases  of  the  blast 
furnace  and  coke  oven. 


*  The  recently  invented  process  of  making  alcohol  from  peat  by  Professor 
Lagerheim  and  Mr.  Frestadius  seems  to  open  up  great  possibilities  in  this 

326 


FUELS  AND  GAS  MAKING  327 

The  solid  fuels  are  transformed,  more  or  less  completely,  into 
permanent  combustible  gases  before  using  in  tne  motor.  The 
cheaper  soft  coals  can  be  utilized  in  this  manner  about  as  well  as 
the  more  expensive  grades.  The  lignites  can  also  be  transformed 
into  satisfactory  power  gas  with  practically  the  same  ease  as 
bituminous  coal.  Even  peat  can  be  dealt  with  in  the  same 
manner.  Wood,  refuse,  straw,  bagasse,  and  other  vegetable 
matter  not  too  wet  can  also  be  used.  Anthracite  coal  is  more 
easily  converted  into  fuel  gas  than  any  other  fuel. 

In  the  transformation  of  solid  fuel  into  power  gas  it  is  desir- 
able, especially  in  power  plants  of  small  and  moderate  capacities, 
to  convert  all  of  the  fuel  part  of  the  solid  combustible  into  per- 
manent gas,  and  thus  avoid  the  formation  of  any  by-products. 
In  a  large  plant,  by-products  can  generally  be  disposed  of  to 
advantage,  but  not  usually  in  those  of  small  power  capacity. 

In  general  there  are  in  common  use  two  types  of  producers 
for  converting  solid  fuel  into  permanent  gas  for  power  purposes. 
The  distinguishing  features  are  that  in  one  type  pressure  pro- 
duced by  auxiliary  apparatus  is  used  to  force  air,  or  steam,  or 
both  together,  through  the  bed  of  solid  fuel;  and  in  the  other  the 
air  and  water  are  drawn  through  by  the  suction  of  the  motor 
itself,  or  of  an  auxiliary  "exhauster."  In  the  pressure  producer 
the  gas  is  made  at  a  more  or  less  uniform  rate  while  the  producer 
is  operating,  and  the  gas  is  stored  in  tanks,  generally  of  small 
capacity,  from  which  it  is  drawn  to  meet  the  varying  needs  of 
the  motor.  In  the  suction  producer  plant  without  auxiliary 
exhauster  there  is  no  storage  of  gas.  The  gas  is  generated  at 
the  rate  that  the  motor  demands  it,  stroke  by  stroke.  When  the 
motor  stops,  the  generation  of  gas  stops  with  it. 

In  the  methods  especially  applied  to  making  power  gas  from 

field  on  account  of  the  small  cost  at  which  the  alcohol  can  be  produced  and 
the  fact  that  all  necessary  materials  for  the  process,  except  sulphuric  acid 
exist  in  some  of  the  immense  peat  swamps  of  the  United  States.  See  Engineer- 
ing Magazine,  August,  1908. 

The  improved  method  of  recovering  sulphuric  acid  during  the  reduction 
of  copper  ore  etc.,  recently  adopted  by  the  Ducktown  Copper  Company  of 
Ducktown,  Tennessee,  makes  possible  the  use  of  sulphuric  acid  on  a  com- 
mercial basis  for  the  production  of  alcohol  from  peat. 


328 


THE  GAS  ENGINE 


FIG.  114. 


FUELS  AND   GAS  MAKING  329 


FIG.    114. 

Continuous  Updraught  Gas  Producer  for  Bituminous  Coal  with  Automatic  Feed. 
Air-and- Water  Gas  Process.  Pressure  or  Suction  Draught.  R.  D.  Wood  & 
Co.,  Philadelphia,  Pa. 

The  fuel  is  charged  on  from  the  small  hopper  at  the  top  with  conical  bottom.  The 
vertical  shaft  of  the  automatic  feed  passes  through  the  central  part  of  the  hopper 
and  has  a  worm-wheel  at  the  top  for  power  driving  by  means  of  the  intermesh- 
ing  worm.  The  fuel-distributing  device  is  attached  to  the  bottom  of  the  vertical 
shaft  and  is  so  shaped  as  to  distribute  the  fuel  evenly  over  the  fuel  bed. 

The  blast  enters  at  the  bottom  through  the  central  pipe  and  passes  out  from  under 
the  small  hood  into  the  ash  and  then  up  into  the  fuel.  The  blast  is  caused  either 
by  a  steam  jet  or  a  mechanical  blower.  In  either  case  steam  enters  with  the  air. 

The  ash  bed  is  supported  on  a  revolving  table  which  can  be  rotated  by  means  of 
the  hand  crank,  pinion  and  spur  gear  outside  of  the  ash  pit,  and  the  small  bevel 
gear  that  meshes  with  the  large  bevel  gear  on  the  under  side  of  the  table.  The 
rods  projecting  from  the  outside  into  the  ash  just  above  the  revolving  table  are 
for  scraping  the  ash  from  the  table  as  it  revolves;  they  are  adjustable  as  to  the 
distance  they  extend  into  the  ash. 

The  gas  passes  out  through  the  side  flue  near  the  top  of  the  gasification  chamber. 
The  ash  pit  is  tightly  closed  while  the  blast  is  on. 

Small  holes  for  observing  and  poking  the  fuel  are  provided  at  the  top  and  sides. 

This  producer  is  practically  the  same  as  that  used  in  the  tests  at  St.  Louis  by  the 
U.  S.  Geological  Survey,  operated  as  a  pressure  producer.  One  of  these  tests 
was  run  562  hours  continuously.  See  Chap.  XXL 


330 


THE   GAS  ENGINE 


FIG.  114a. 


FUELS  AND   GAS  MAKING  331 


FIG.    114a. 

Continuous  Updraught  Pressure  Producer  for  Bituminous  Coal,  with  Automatic 

Feed  and  Water-sealed  Ash  Pit.     Either  Pressure   or  Suction   Draught. 

R.  D.  Wood  &  Co.,  Philadelphia,  Pa. 

This  is  much  the  same  as  the  producer  shown  in  Fig.  114  except  the  water  seal  at 
the  bottom.  This  method  of  closing  the  ash  pit  allows  the  removal  "of  ashes 
while  the  blast  is  on,  and  thus  the  continuous  operation  of  the  producer  for  an 
indefinite  period  without  cutting  off  the  blast. 

The  pipe  for  carrying  the  steam  to  the  jet  that  produces  the  blast  is  shown  at  the 
lower  left-hand  side. 

A  producer  of  this  general  type,  without  the  automatic  feed,  is  in  use  at  the  works 
of  the  American  Locomotive  Co.,  Richmond,  Va.  A  test  of  the  gas  power  plant 
at  these  works  is  reported  in  the  Proc.  Amer.  Inst.  Elec.  Engrs.,  July,  1908. 


332  THE   GAS  ENGINE 

solid  fuel,  the  process  is  either  one  of  burning  the  fuel  with  so 
small  a  supply  of  air  that  only  incomplete  combustion  takes  place 
with  the  production  of  combustible  gases,  or  one  in  which  water 
vapor  or  steam  is  brought  into  contact  with  the  hot  fuel  and  the 
fuel  and  steam  act  mutually  on  each  other  so  that  fuel  gas  is 
formed.  Both  methods  are  often  applied  simultaneously  to  the 
fuel.  The  only  solid  matter  left  in  any  appreciable  quantity  is 
the  ash.  In  some  methods  practically  all  of  the  combustible  of 
the  fuel  is  converted  into  permanent  gas.  In  others  an  appreciable 
quantity  of  semi-liquid  matter  is  formed  by  the  condensation  of 
some  of  the  gas.  This  is  abstracted  from  the  gas.  Some  of  the 
methods  of  making  gas  for  illuminating  purposes  differ  radically 
from  those  for  power  gas. 

The  heat  values  per  cubic  foot  of  the  combustible  mixtures 
formed  by  mixing  different  fuels  with  air  are  different.  For 
example,  a  mixture  of  blast-furnace  gas  and  air  has  only  about 
60  per  cent  of  the  amount  of  heat  available  per  cubic  foot  that  a 
mixture  of  gasoline  vapor  and  air  has,  both  mixtures  being 
proportioned  for  perfect  combustion.  And  a  mixture  of  illuminat- 
ing gas  and  air  has  about  90  per  cent  of  the  heat  value  of  the 
gasoline  vapor  and  air  mixture,  both  mixtures  taken  at  the  same 
volume,  temperature,  and  pressure. 

The  power  that  a  motor  will  develop  is  in  a  measure  proportional 
to  the  lower  heat  value  per  cubic  foot  of  the  combustible  mixture 
used  (but  not  to  either  the  lower  or  the  higher  heat  value  of  the 
fuel  gas).  If  the  compression  pressure  is  kept  the  same  for  all 
mixtures,  then  the  power  capacity  of  the  motor  on  the  different 
mixtures  is  nearly  proportional  to  the  heat  value  of  the  mixture. 

A  motor  that  is  to  develop  a  certain  amount  of  power  at  a  given 
speed  of  piston  travel  must  be  considerably  larger  in  cylinder 
capacity  for  blast-furnace  gas  than  for  natural  gas,  illuminating 
gas,  gasoline,  naphtha,  kerosene,  or  fuel  oil.  The  compression 
pressure  can  be  carried  considerably  higher  for  blast-furnace  gas 
than  for  the  other  fuels  just  mentioned.  Since  the  higher  com- 
pression pressure  increases  the  efficiency  of  heat  transformation 
into  mechanical  energy,  the  ratio  of  the  cylinder  capacity  of  the 
motor  using  blast-furnace  gas  to  that  of  the  one  using  natural 


FUELS  AND   GAS  MAKING  333 

gas  is  therefore  somewhat  less  for  the  same  power  developed  than 
the  ratio  of  the  lower  heat  value  of  the  natural  gas  and  air  mixture 
to  that  of  the  blast-furnace  gas  and  air  mixture. 

221.  Retort  Gas  by  Distillation  of  Bituminous  Coal.  Coal 
Gas.  —  Bituminous  coal  (soft  coal)  is  placed  in  a  retort  which  is 
then  tightly  closed  except  where  a  pipe  is  connected  for  carrying 
off  the  gas.  An  external  fire  heats  the  retort  to  incandescence 
and  drives  off  from  one-fourth  to  one-third  of  the  coal  as  gas, 
according  to  the  grade  of  coal  used.  The  gas  is  passed  through 
a  water-cooled  pipe,  where  some  .of  the  unstable  gas  is  condensed 
to  the  form  of  tar.  The  remaining  gases  are  still  further  cooled, 
washed  with  water,  and  chemically  treated  to  remove  the  remain- 
ing tar  vapors,  ammonia  vapor,  carbon  dioxide,  sulphur,  and  any 
other  impurity  that  may  be  present.  If  the  coal  is  of  a  certain 
composition,  the  resulting  gas  is  suitable  for  illuminating  pur- 
poses when  burned  as  an  open  flame.  But  when  there  are  not 
enough  illuminants  present  in  the  distilled  gas  it  is  enriched  with 
illuminants,  generally  from  petroleum  or  petroleum  products. 
Two-thirds  to  three-quarters  of  the  weight  of  the  coal  remains 
in  the  retort  as  coke,  composed  of  carbon  and  earthy  matter. 
The  principal  by-products  of  the  retort  process  are  coke  (gas 
coke),  tar,  and  ammonia.  These  and  the  other  by-products  are 
converted  into  almost  innumerable  other  substances  by  suitable 
processes. 

The  composition  of  retort-distilled  gas  varies  with  both  the  kind 
of  coal  used  and  the  temperature  (or  rapidity)  of  distillation. 

Assuming,  for  a  very  rough  method  of  comparison  between 
the  heat  value  of  the  gas  distilled  and  of  the  coal,  that  each  pound 
of  coal  gives  5  cubic  feet  of  gas  having  a  heat  value  of  600  B.t.u. 
per  cubic  foot  before  enriching,  which  is  a  high  value,  and  that 
the  heat  value  of  the  coal  is  15,000  B.t.u.  per  pound,  it  will  be 
seen  that  only  twenty,  per  cent  of  the  heat  of  the  coal  appears  in 
the  gas. 

While  retort  gas  made  as  just  described  burns  with  entire 
satisfaction  in  the  combustion  motor,  it  is  too  expensive  for  use 
in  large  motors  on  account  of  the  method  of  production  and  the 
high  grade  of  coal  that  must  be  used.  This  refers  especially  to 


334  THE  GAS  ENGINE 

power  plants  of  medium  size  where  recovery  of  by-products  is 
not  commercially  advantageous. 

The  other  extreme  point  of  view  is  that  a  coal-distilling  plant 
may  be  operated  with  gas  as  a  by-product,  and  the  other  sub- 
stances produced  as  the  valuable  commodities  sought.  This 
condition  is  realized  in  the  manufacture  of  coke  and  the  use  of 
the  excess  gas  for  combustion  motors. 

222.  Air  Gas  by  Burning  Solid  Fuel  with  Insufficient  Air.  — 
While  this  method  is  not  used  for  producing  gas  for  power  pur- 
poses, it  will  be  described  because  various  combinations  of  it  and 
the  water-gas  process  (to  be  described  later)  constitute  practically 
all  the  commercial  methods  of  manufacturing  power  gas  (and  also 
fuel  gas  for  furnaces). 

The  air-gas  process  is  similar,  in  a  way,  to  incomplete  com- 
bustion in  a  furnace  whose  function  is  to  produce  heat.  This  is 
such  a  condition  as  exists,  to  some  extent,  when  the  fuel  bed  is 
carried  too  thick  or  too  deep  for  heating  purposes.  In  such  a 
case  the  products  of  combustion,  especially  when  anthracite  coal 
or  coke  is  used  as  a  fuel,  contain  a  large  percentage  of  carbon 
monoxide,  CO. 

In  the  simpler  forms  of  air-gas  producers  in  which  air  enters 
the  fuel  bed  at  the  bottom  and  passes  off  at  the  top,  there  is 
generally  a  considerable  thickness  of  ash  between  the  burning 
fuel  and  the  grate  bars  or  other  device  for  supporting  the  charge. 

When  the  air  comes  into  contact  with  the  incandescent  carbon, 
the  O  of  the  air  and  some  of  the  carbon  unite  to  form  either  CO 
or  CO2.  Just  what  the  chemical  reactions  are  has  never  been 
determined.  The  resulting  gases  that  pass  from  the  fuel  contain 
both  CO  and  CO2  under  ordinary  conditions  of. operating  a 
producer.  Since  the  CO2  is  not  combustible,  the  process  is 
carried  out  so  as  to  cause  the  C  to  combine  with  the  O  as  CO  as 
far  as  possible. 

Most  of  the  heat  liberated  by  the  burning  of  the  carbon  goes 
to  raise  the  temperature  of  the  products  of  combustion  and  is 
carried  from  the  producer  by  the  gas.  A  small  proportion  goes 
to  raise  the  temperature  of  the  fuel,  to  vaporize  the  .volatile  part, 
and  to  balance  the  heat  lost  by  radiation,  etc. 


FUELS  AND   GAS  MAKING  335 

There  is  generally  an  appreciable  amount  pf  water  vapor 
(moisture)  in  the  air.  The  coal  contains  water,  or  hydrogen 
and  oxygen  in  the  proportion  to  form  water,  sometimes  to  the 
extent  of  several  per  cent  of  its  weight.  But  even  with  the  cooling 
effects  of  atmospheric  and  fuel  moisture,  radiation  and  excess  of 
air,  and  other  causes,  the  temperature  of  the  gases  passing  from 
the  fuel  is  high.  The  complete  combustion  of  some  of  the  carbon 
which  occurs  keeps  the  temperature  higher  than  that  of  incom- 
plete combustion  alone. 

When  bituminous  coal  is  used  in  the  gas  producer,  the  volatile 
parts  are  first  distilled  off  in  much  the  same  manner  as  in  the 
retort  process,  so  far  as  the  action  on  the  coal  is  concerned.  The 
coke  thus  formed  is  then  burned  by  the  oxygen  of  the  air.  Tar 
and  ammonia  products,  etc.,  are  formed  as  in  the  retort  process, 
unless  the  generator  is  especially  constructed  to  dissociate  the 
unstable  gases  and  allow  recombination  of  their  elements  into 
stable  gases.  This  latter  action  will  be  taken  up  in  connection 
with  the  processes  more  suitable  for  making  power  gas. 

A  large  amount  of  heat  is  carried  from  the  fuel  by  the  gases  in 
the  air-gas  process.  This  heat  can  be  utilized  to  some  extent  for 
heating  the  air  going  to  the  producer,  but  still  the  gas  will  be  very 
hot  even  after  the  heat  for  this  purpose  has  been  abstracted. 

The  gas  must  be  washed  and  otherwise  purified  before  going 
to  the  motor.  This  has  the  effect  of  cooling  it.  The  major  part  of 
the  heat  that  is  carried  from  the  producer  by  the  gas  is  thus  lost 
unless  unusual  means  are  provided  to  utilize  it  for  purposes  other 
than  for  the  motor.  On  account  of  this  great  waste  of  heat  the 
simple  air-gas  process  is  not  economical  for  generating  power  gas. 

The  theoretical  value  of  all  the  heat  that  can  be  obtained  by 
chemically  accurate  carrying  out  of  the  air-gas  process  when  the 
fuel  is  assumed  to  be  pure  carbon,  can  be  determined  as  follows : 

Bt.u. 

Heat  value  of  i  pound  C  burned  to  CO2 14650 

Heat  liberated  by  burning  i  pound  C  to  CO 4206 

Heat  in  2j  pounds  CO  produced  =  14650—4206  =  10444 

Ratio  of  heat  value  of  total    )  _  10444  _         _ 

CO  produced  to  that  in  the  C  \  ~  14650  ~'713  ~?I'3  PC 


336  THE  GAS  ENGINE 

This  is  the  theoretical  limit  of  the  efficiency  of  the  air-gas  proc- 
ess with  pure  dry  carbon  and  no  moisture  in  the  atmosphere. 

The  theoretical  efficiency  of  the  air-gas  process  with  coals  con- 
taining volatile  matter  will  in  general  be  somewhat  different  from 
the  value  just  obtained.  Moisture  in  the  fuel  and  the  atmosphere 
also  modifies  this  efficiency. 

223.  Water  Gas  in  General.  —  Water  gas  is  made  by  bringing 
steam  into  contact  with  highly  heated  fuel.  The  steam  is  decom- 
posed into  its  elements,  H  and  O,  and  the  O  then  combines  with 
the  C  of  the  fuel  to  form  carbonic  oxide,  CO.  The  hydrogen 
escapes  as  free  H.  This  is  when  the  only  combustible  in  the  fuel 
is  C  and  the  process  is  theoretically  perfect.  In  practice  some 
carbonic  acid,  CO2,  is  also  formed.  There  are  also  other  com- 
bustible substances  generally  present  in  the  gas  formed  on  account 
of  impurities  and  hydrocarbons  in  the  fuel. 

The  chemical  equations  representing  the  theoretical  process  of 
water-gas  formation  from  the  carbon  constituent  of  the  fuel  are: 

2    VOl.  2    VOl.  2    VOl. 

2  H2O  +  C2  =  2  CO  +  2  H2, 

H20  +  C    =     CO  +  2  H 

1 8          12          28       2          Weight  proportions. 
Pounds  1  f  -V-      i 

The  last  two  equations  show  that  the  volumes  of  CO  and  H 
produced  are  equal  to  each  other,  and  that  the  total  volume  of  the 
combustible  gas  produced  is  twice  that  of  the  steam  used,  dealing 
with  equal  temperatures  and  pressures. 

The  equations  also  show  that  the  weight  of  the  CO  produced  is 
fourteen  times  that  of  the  H  that  is  set  free. 

There  are  two  distinct  methods  of  manufacturing  water  gas. 
One  is  known  as  the  continuous  or  retort  process,  and  the  other 
is  an  intermittent  process.  The  retort  process  is  but  little  used. 
The  intermittent  process  finds  a  large  field  of  application. 

There  is  also  a  process  of  alternately  making  air  gas  and 
water  gas  in  a  producer.  It  is  only  a  slight  modification  of  the 
intermittent  water-gas  process,  and  finds  broad  application. 


FUELS  AND   GAS    MAKING  337 

Water  gas  does  not  give  an  illuminating  flame,  s^ince  it  contains 
little  or  none  of  the  heavy  hydrocarbons  which,  as  has  been  stated, 
are  the  illuminating  constituents  of  a  gas.  Water  gas  can  be 
made  illuminating  by  carbureting  by  the  addition  of  heavy 
hydrocarbons.  This  is  generally  done  by  adding  to  it  the 
heavy  hydrocarbon  gases  of  petroleum,  obtained,  in  some  cases 
at  least,  by  decomposing  the  heavy  distillates  of  petroleum 
by  heat.  Carburation  increases  the  cost  of  production  per 
cubic  foot. 

The  three  processes  which  have  been  mentioned  in  this  section 
will  be  separately  discussed  later. 

224.  Producer   Gas    by   Combined   Air-Gas    and    Water-Gas 
Processes.  —  The  gas  intended  especially  for  power  (and  heating) 
purposes  is  practically  all  made  by  processes  that  are  combinations 
of  the  air-gas  and  water-gas  processes.   There  are  several  different 
ways  in  common  use  for  combining  these  two  processes.     One 
method  is  to  admit  both  air  and  steam  or  water  vapor  simulta- 
neously and  continuously  to  the  fuel,  thus  producing  continuously 
a  mixture  of  air-  and  water-gas.     Another  method  is  to  burn  the 
fuel  with  air  for  a  while  till  the  fuel  bed  has  become  highly 
incandescent,  and  then  to  cut  off  the  air  and  pass  steam  or  water 
vapor  into  the  hot  mass,  alternating  the  periods  of  air  and  water 
admission  so  as  to  keep  the  temperature  of  the  fuel  within  a  range 
suitable  for  satisfactorily  carrying  on  the  manufacture  of  the  gas. 
Air  gas  is  made  during  the  period  of  "  bio  wing"  while  the  air 
alone  is  admitted,  and  water  gas  only  during  the  "run"  while 
steam  alone  is  admitted. 

The  name  "producer  gas"  is  quite  generally  understood  to 
mean  the  mixture  of  air-  and  water-gas  made  by  any  of  these 
processes,  but  it  is  also  applied  sometimes  to  air  gas  alone  and 
sometimes  to  water  gas  alone. 

225.  Suction  Producer  for  Anthracite  Coal  or  Coke.     Suction 
Due  to  Intake  Stroke  of  Motor  Piston.  —  Power  gas  for  motors 
up    to   three   hundred   horsepower  can   be   made    satisfactorily 
by  drawing  air  and  steam  or  water  vapor  by  suction  through  a 
deep  bed  of  anthracite  coal.     The  more  common  form  of  suction 
producer  is  a  vertical  cylinder  of  metal  lined  with  fire-brick.     The 


338  THE  GAS  ENGINE 

fuel  is  supported  by  a  grate  or  some  other  form  of  rest  that  partly 
fills  the  lower  part  of  the  enclosed  space,  leaving  a  circular  opening 
near  the  wall  through  which  the  ash  can  drop  out.  The  producer 
is  closed  air  tight  except  the  openings  for  admitting  air  and  steam 
and  another  for  the  escape  of  the  gas.  In  the  usual  forms  the 
suction  of  the. motor  draws  air  and  steam  or  water  vapor  through 
the  fuel,  where  the  chemical  changes  of  dissociating  the  steam 
and  burning  the  coal  take  place.  In  one  type  of  suction  producer 
plant  the  gases  pass  from  the  producer  to  an  economizer  and 
there  give  up  part  of  their  heat  for  warming  the  air  that  is  going 
to  the  producer,  and  also  to  vaporize  the  water  to  supply  the 
requisite  amount  of  steam  to  the  producer.  The  gases  then  pass 
into  the  bottom  of  a  scrubber  for  cleaning  the  gas  by  washing  it 
with  water.  The  scrubber  is  generally  a  vertical  cylinder  filled 
with  rather  finely  broken  coke,  or  having  a  large  number  of  wood 
slats,  etc.,  over  and  through  which  water  trickles  from  the  top 
to  the  bottom.  The  gas  is  freed  more  or  less  completely  from 
soot,  dust,  and  some  of  the  other  impurities  while  passing  upward 
through  the  scrubber.  From  the  top  of  the  scrubber  the  gas  goes 
into  a  purifier,  dry  cleaner,  or  moisture  separator,  in  which  it 
passes  through  some  finely  divided  substance  such  as  sawdust 
or  fine  wood  shavings,  for  final  cleaning  and  freeing  from  mois- 
ture and  solid  particles.  From  the  purifier  the  gas  goes  directly 
to  the  motor  cylinder  in  the  required  amount  during  the  charg- 
ing stroke  of  the  piston.  A  small  drum  is  sometimes  placed 
between  the  motor  and  the  purifier.  It  provides  a  mass  of 
gas  for  expanding  and  flowing  into  the  motor  during  the  suc- 
tion stroke,  thus  maintaining  a  more  steady  flow  through  the 
producer  and  its  accessories  and  offering  less  resistance  to  the 
suction  of  the  motor  than  when  no  such  drum  is  used. 

The  air  going  to  the  producer  passes  through  the  economizer, 
where  it  receives  heat  from  the  producer  gas  before  entering  the 
ash  pit  or  air  space  of  the  producer.  The  steam  from  the  vapor- 
izer also  passes  into  the  sealed  ash  pit,  from  which  the  mingled 
air  and  steam  are  drawn  into  the  fuel. 

The  function  of  the  economizer  is  to  utilize  as  much  as  possible 
the  heat  carried  from  the  producer  by  the  gases. 


FUELS  AND   GAS  MAKING  339 

The  exhaust  from  the  motor  is  sometimes  utilized  for  pre- 
heating the  air  that  goes  to  the  producer. 

The  theoretical  changes  that  take  place  in  the  producer  are  the 
incomplete  combustion  of  a  part  of  the  carbon  of  the  fuel  by  the 
oxygen  of  the  air  to  form  CO;  the  decomposition  of  the  steam 
into  its  elements  H  and  O;  and  the  combination  of  the  O  thus 
liberated  with  the  remainder  of  the  carbon  to  form  more  CO. 

The  decomposition  of  the  steam  absorbs  sensible  heat  in  a 
larger  amount  than  is  liberated  by  the  combustion  of  its  O  with 
the  C  to  form  CO.  Heat  is  therefore  required  for  the  water-gas 
part  of  the  process  of  gas  generation. 

The  air-burned  part  of  the  fuel  supplies  the  heat  necessary 
for  the  water-gas  part  of  the  process,  and  also  the  heat  carried 
off  by  the  gas,  lost  by  radiation,  required  to  heat  the  fuel,  etc. 

Since,  in  the  suction  producer  direct  connected  to  the  motor 
as  described,  the  demand  for  gas  varies  with  the  amount  of  power 
that  the  motor  must  furnish  at  any  moment,  and  because  the 
temperature  of  the  fuel  bed  should  remain  nearly  constant,  it  is 
evident  that  the  rate  of  supplying  steam  to  the  fuel  bed  must  be 
variable  in  somewhat  the  same  proportion  as  the  rate  at  which 
gas  is  generated.  Automatic  regulation  of  the  amount  of  steam 
supplied  therefore  becomes  a  necessity  for  the  direct-connected 
suction  gas  producer. 

The  construction  of  the  gas-generating  plant  just  described  is 
such  as  to  secure  automatic  control  of  the  steam  supply.  In  it 
as  long  as  the  gas  is  generated  at  a  certain  rate  the  steam  will  be 
formed  at  a  practically  constant  corresponding  rate,  for  if  the 
temperature  of  the  fire  and  the  gas  passing  from  it  should  rise, 
the  gas  will  carry  more  heat  to  the  water  in  the  vaporizer  and  the 
rate  of  steaming  will  consequently  be  increased.  The  increased 
amount  of  steam  will  in  turn  cool  the  fire  down  to  the  proper 
temperature.  A  reverse  action  occurs  when  the  fire  tends  to 
get  too  cool. 

Again,  when  the  load  on  the  motor  increases,  more  air  is  drawn 
into  the  generator  than  before.  The  increased  amount  of  air 
increases  the  temperature  of  the  fire  slightly,  and  the  greater 
amount  of  slightly  warmer  gas  carries  more  heat  over  to  the 


340  THE   GAS  ENGINE 

vaporizer,  so  that  more  steam  is  formed  to  keep  both  the  tem- 
perature and  the  composition  of  the  gas  constant.  The  reverse 
occurs  when  the  load  on  the  motor  decreases. 

In  some  designs  of  suction  producers  the  vaporizer  is  part  of  the 
producer.  The  water  space  in  such  cases  is  generally  over  the 
top  and  around  the  upper  part  of  the  generator. 

The  steam  is  sometimes  admitted  to  the  fuel  some  distance 
above  the  bottom  of  the  fire.  This  is  done  to  secure  the  most 
complete  consumption  of  the  fuel  by  allowing  only  air  to  come 
in  contact  with  it  at  the  lowest  zone  of  combustion  and  thus  to 
maintain  a  high  temperature  while  the  last  of  each  piece  of  fuel 
is  consumed.  The  fact  that  considerable  coal  passes  unburned 
into  the  ash  in  some  types  of  producers  makes  it  essential  to 
consider  some  means,  as  that  just  mentioned,  for  the  prevention 
of  fuel  waste  in  this  manner. 

For  starting  the  fire  in  a  suction  producer  of  the  size  and  type 
under  discussion,  or  for  bringing  up  the  fire  after  it  has  been  idle 
for  some  time,  as  over  night  or  a  holiday,  an  air  blower  is  necessary. 
When  the  blower  is  hand  operated,  which  is  generally  the  case  for 
the  small  plants,  the  plant  is  entirely  independent  of  any  other 
source  of  power.  While  blowing  up  the  fire  a  vent  is  opened 
between  the  producer  and  scrubber  to  allow  the  gas  to  pass  off. 
The  vent  is  generally  between  the  economizer  and  scrubber. 
When  the  vent  is  thus  located,  the  economizer  is  heated  during 
the  period  of  blowing  up  the  fire. 

226.  Theoretical  Case  of  Gas  Producer.  —  A  convenient 
method  of  following  out  the  operations  of  a  gas  producer  operating 
continuously  in  the  manner  of  the  suction  type  described  in  the 
preceding  section,  is  to  assume  that  there  is  neither  loss  of  heat 
by  radiation,  carrying  off  by  the  gas,  etc.,  nor  gain  of  heat  from 
energy  supplied  by  any  exterior  source.  Such  a  case  cannot 
possibly  exist,  of  course.  But  this  manner  of  simplifying  the 
operations  of  the  process  warrants  such  assumptions  in  order 
to  secure  ready  means  for  following  out  the  essential  parts  of 
the  process. 

It  will  therefore  be  assumed,  for  the  purpose  jast  stated,  that 
the  producer  delivers  gas  at  the  same  temperature  and  pressure 


FUELS  AND   GAS  MAKING  341 

as  that  of  the  atmosphere,  that  there  is  no  heat  loss  by  radiation, 
and  that  the  gain  of  heat  on  account  of  the  energy  consumed  in 
creating  a  draft  through  the  apparatus  is  just  balanced  by  the 
loss  in  the  heat  carried  off  by  the  ash. 

Under  such  assumptions  the  total  heat  value  of  the  gas  pro- 
duced is  the  same  as  that  of  the  fuel  consumed.  The  com- 
putations which  are  given  below  deal  with  the  gas  produced 
from  a  pound  of  carbon  burned  by  the  combined  air-  and  water- 
gas  process. 

227.  Computations  for  Theoretical  Gas  Producer.  —  Supplies 
received  and  products  delivered  at  62°  F.  and  14.7  pounds  per 
square  inch  pressure. 

Higher  heat  values  used. 

Heat  liberated  by  i  Ib.  C  burned  to  CO2 4206  B.t.u. 

Heat  required  to  vaporize  and  decompose  i  Ib. 

water  =  61,984  4-9= 6887  B.t.u. 

Heat  liberated  by  burning  two-thirds  Ib.  C  to 
CO  with  the  eight-ninths  pound  O  liberated 
by  the  decomposition  of  i  Ib.  of  water  =  §  X 

4206  = 2804  B.t.u. 

(See  section  223  and  table  of  heat  values.) 

Heat  to  be  supplied  by  air-burned  C  for  main- 
taining a  uniform  temperature  of  the  fuel  while 
i  Ib.  water  is  decomposed  and  its  O  united 
with  C  to  form  CO  =  6887  -  2804  = 4083  B.t.u. 

Water  per  pound  of  air-burned  C  that  will 


keep  the  temperature  of  the  fuel  bed 


-,  4083 

uniform 


4206 


=  1.0301  Ibs. 


Carbon  burned   by  O  from  above   amount   of 
water  =  1.0301  X  §  = 6867  Ib. 

Total  C  burned  for  each  pound  of  air-burned  C      i  .6867  Ibs. 

Water  dissociated  and  resulting  O  com-]  _ 
bined  with  C  per  Ib.  of  C  burned. 

Percentage   of  air-burned  C  =  I0°  X  I  =  ...  .59.29  per  cent. 

1.6867 

Percentage  of  water-burned  C=  I0°  X  '6867  =  40.71  percent. 

1.6867 


:om-|=_L.o3oi_= 
[.      j      i  +  .6867 


342  THE   GAS   ENGINE 

For  the  air  -burned  part  oj  1  pound  carbon. 

Pounds    Cubic  Feet 

Air-burned  part  of  1  Ib.  C  ...................  .593  ..... 

Air  for  burning  .593  Ib.  C  =  .593  X  5.76  =  .  .  .  3.415  44.8 

CO  formed  by  air  burning  =  2\  X  .5928=  .,U  1.383  18.83 

(1  Ib.  C  forms  i\  Ibs.  CO.) 

N  from  air  burning  =  3.415  X  .7688  ..........  2.625  35.51 

Total  products  from  air-burned  part  of  1  Ib.    C  4.008  54-34 
Total  heat  value  of  air  gas  from  air-burned  part 

of  1  Ib.  carbon  =  1.383  X  4476  =  ......  '  ...........  6190  B.t.u. 

B.t.u.  per  cubic  foot  of  air  eras  =  —  "  —  =  .............  TIA  B.t.u. 


For  the  water  -burned  part  of  1  pound  carbon. 

Pounds         Cubic  Feet 

Water-burned  part  of  1  Ib.  C  ..................  4071         ..... 

Water  used  for  burning  .4071  Ib.  C  ............  6107         .^TTT^ 

CO  formed  by  water  burning  =  2^  X  .4071  =      .9500          12.93* 

Hsetfree  =  ^2=  .........................  0679          12.85* 

9 

Total  product  from  water-burned  part  of  1  Ib.  C  =  i  .0179         25.78 
Heat  value  of  CO  from  water-burned  part  of 

1  Ib.  C  =  .95  X  4476  =  ..........................  4252  B.t.u. 

Higher  heat  value  of  H  from)      ^6107  x  6     ^  =     ^  fi  t  u 


water-burned  part  of  1  Ib.  CJ  9 

Total  higher  heat  value  of  water  gas  from  water-burned 

part  of  1  Ib.  C  =  4252  +  4206  =  ................     8458  B.t.u. 

O   .  -Q 

B.t.u.  (higher)  per  cubic  foot  of  water  gas  =  —  —  —  =      328  B.t.u. 

25  .78 

*  According  to  the  volumetric  relations  in  the  chemical  equation  for  water- 
gas  formation,  the  volume  of  H  =  volume  of  CO.  This  result  is  not  obtained 
in  the  computations,  partly  at  least  on  account  of  using  the  approximate 
atomic  weights  in  the  application  of  the  equations  in  connection  with  tabular 
values  that  are  based  on  the  accurate  atomic  weights.  The  atomic  weight  of 
H  is  taken  as  1  in  the  computations,  while  its  accurately  determined  and 
accepted  value  is  1.008. 


FUELS  AND   GAS  MAKING 


343 


For  burning  1  pound  carbon  to  CO  by  the  combined  air-  and 
water-gas  process;  theoretical  case  of  100  per  cent  efficiency. 


PRODUCTS. 


Weight  of 

Volume  Each 

Heat  Value  of 
Each  Product 

Perce 

ntage. 

Each  Product. 
Lbs. 

Product. 
Cu.  Ft. 

B.t.u. 
Higher. 

By  Weight. 

By  Volume. 

CO  

2  .  T.T.T. 

3I-76 

10,444 

46.42 

30-  64 

H  
N  

.068 
2  .  62? 

12.85 
35.51 

4,206 

?-35 

(52.23 

16.04 

44.  72 

Totals  .  . 

5.020 

80.12 

14,650 

IOO.OO 

IOO.OO 

Air  used  in  producer  per  Ib.  of  carbon  =  3.45  Ibs.  =  44.8  cubic  feet. 
Water  used  in  producer  per  Ib.  of  carbon  =  .6107  Ib. 

Higher  heat  value  of  gas  produced  =  I4'  ^°  =183  B.t.u.  per  cubic 

80.12 

foot. 

Specific  heat  of  gas  produced  =  .288  B.t.u.  per  Ib.  at  constant  pressure. 

Air  per  cubic  foot  of  gas  for  perfect  combustible  mixture  (.3964  + 
.1614)  2.39  =  .5578  X  2.39  =  1.33  cubic  feet. 

B.t.u.  per  cubic  foot  perfect  mixture  =  —  — - —  =78.4  B.t.u. 

The  total  heat  carried  in  by  each  pound  of  carbon  is  14,650 
B.t.u.,  which  is  the  same  as  is  returned  in  the  combustible  gas 
under  the  theoretical  conditions  assumed. 

The  results  obtained  above  can  be  checked  by  comparing 
(a)  the  product  of  the  heat  liberated  by  the  formation  of  1  pound 
of  CO  multiplied  by  the  pounds  of  CO  formed  with  (b)  the 
product  of  the  heat  absorbed  per  pound  of  H  liberated  multiplied 
by  the  pounds  of  H  liberated.  The  two  products  should  be  equal 
for  the  100  per  cent  efficiency  assumed.  The  same  reasoning  is 
true  for  cubic  foot  units  (or  any  other  units). 

The  amounts  of  heat  liberated  or  absorbed  per  unit  of  product 
are  given  below  for  62°  F.  and  14.7  pounds  per  square  inch  pres- 
sure absolute. 


344  THE   GAS  ENGINE 

Heat  liberated  during  the  combination  of: 

C  and  O  to  form  1  cu.  ft.  CO  =  132.5  B.t.u.  per  cu.  ft.  CO. 

C  and  O  to  form  1  cu.  ft.  CO2  =  462.  B.t.u.  per  cu.  ft.  CO2. 

C  and  O  to  form  1  Ib.  CO  =  1803  B.t.u.  per  Ib.  CO. 

C  and  O  to  form  1  Ib.  CO2  =  3995  B.t.u.  per  Ib.  CO2. 

Heat  absorbed  during  the  dissociation  of: 

H2O  to  liberate  1  cu.  ft.  H  =  328  B.t.u.  per  cu.  ft.  H. 
H2O  to  liberate  1  Ib.  H        =  61,984  B.t.u.  per  Ib.  H. 

The  amounts  of  CO  and  H  resulting  from  the  gasification  as 
assumed  above  are  39.64  cubic  feet  CO  and  16.04  cubic  feet  H. 
By  multiplying  these  amounts  by  their  respective  heat  factors, 
just  given,  the  results  are: 

I32-5  X  3J-76  =  4208  B.t.u. 
328     X  12.85  =  4214  B.t.u. 

which  is  as  near  an  agreement  of  values  as  can  be  expected  with 
the  use  of  round  numbers  for  the  heat  values  and  the  other  errors 
due  to  approximate  values. 

Using  pound  units  in  a  similar  manner,  the  results  are: 

1803  X  2.333     =  4206  B.t.u. 
61,984  X    .0679  =  4208  B.t.u. 

The  percentage  composition  can  be  used  in  a  similar  manner, 
the  percentage  of  each  constituent  of  the  gas  being  considered  as 
cubic  feet  in  100  cubic  feet,  or  as  pounds  in  100  pounds  of  the  gas. 

If  the  C  were  burned  to  CO2  in  a  theoretical  case  similar  to 
that  just  considered  when  there  are  no  hydrocarbons  in  the  gas, 
the  relative  amounts  of  CO2  and  H  for  100  per  cent  efficiency  of 
gas  production  are  obtained  from  the  following  equations: 

For  cubic  foot  units, 

328  H  =  462  CO2 ; 
for  pound  units, 

61,984  H  =  3995  C02, 

in  which  the  numerical  quantities  are  the  higher  heat  values  of 
the  gases. 


FUELS  AND   GAS  MAKING 


345 


The  composition  of  suction  producer  gas  from  fuel  that  has 
only  C  as  the  combustible  can  be  determined  from  these  equations 
for  the  theoretical  assumed  case,  as  is  done  below. 

Since  each  pound  of  H  in  the  gas  represents  8  pounds  of  O 
from  the  decomposed  water,  and  each  pound  of  O  combines 
with  twelve-thirty-seconds  of  a  pound  of  C  to  form  CO2  (CO2  =  12 
parts  C  and  32  parts  O  by  weight),  therefore 

For  each  pound  of  H  in  the  gas  produced  there  are  8  X  Jf  = 
3  pounds  C  water-burned  to  CO2. 

Heat  liberated  in  burning  3  Ibs.  C  to  CO2  X  145650  =4390  B.t.u. 
Heat  to  be  supplied  by  air-burned  C  for  each  Ib.  of 

H  in  the  gas  produced  =  61,984  —  43,95°  =  •  •    18,034  B.t.u. 

Pounds  of  air-burned  C  =  l8'°34  = 1.231  Ibs.  C 

14,650 

Total  C  burned  per  Ib.  of  H  in  the  gas  =  3  +  1.231  =4.231  Ibs.  C 
Nitrogen  carried  in  with  air  for  air-burning  1.231 

Ibs.  C  =  1.231  X8.86  = 10.9  Ibs.  N 

Lbs.  CO2  from  4.231  Ibs.  C  =  4.231  X  3§  =  ....    15.515  Ibs.  CO2 

Composition  of  Gas  when  C  is  Burned  to  C02  by  the 
Combined  Air-  and  Water-Gas  Processes. 

Theoretical  case  of  100  per  cent  efficiency. 


Weights. 

Volumes. 

Percentage 

Percentage 

by  Weight. 

by  Volume. 

fc:: 

N  

I5-5I4 

I.  000 

10.906 

134.2 
189.4 
147.6 

56.58 
3.65 
39-77 

28.48 
40.20 
3I-32 

Totals 

27.320 

471-2 

100.00 

100  .  00 

The  weights  and  volumes  per  Ib.  of  C  burned  can  be  obtained  by 
dividing  by  4.231. 

Pounds  of  gas  produced  per  Ib.  of  C  =  2?-32  =6.46  Ibs.  gas. 

4.231 


Cu.  ft.  of  gas  produced  per  Ib.  of  C 


4.231 


111.4  cu.  ft.  gas. 


Hydrogen  produced  per  Ib.  of  C  =      9'4   =  44.7  cu.  ft.  H. 

4.231 


346  THE  GAS  ENGINE 

Heat  value  of  H  liberated  per  Ib.  of  C.  burned  =  44.7  X  328  = 
14,650  B.t.u.  about. 

Higher  heat  value  of  gas  for  40.2  per  cent  H,  which  is  the  only  com- 
bustible, =  .402  X  328  =  131.8  B.t.u.  per  cu.  ft. 

Specific  heat  of  gas  produced  =  .345  B.t.u.  per  Ib.  at  constant  pressure. 

Air  per  cu.  ft.  of  gas  for  perfect  mixture  =  .402  X  2.39  =  .96  cu.  ft. 

B.t.u.  per  cu.  ft.  of  perfect  mixture  =     I*1' —  =67  B.t.u.  higher. 

i  +  .96 

A  comparison  of  the  above  two  cases  shows  that  both  the  gas 
produced  and  the  perfect  mixture  have  higher  heating  values  per 
cubic  foot  when  the  carbon  is  burned  to  CO  than  when  it  is 
burned  to  CO2.  There  is  a  smaller  quantity  of  gas  in  the  former 
case,  however,  so  that  the  total  heat  values  of  the  gas  produced 
from  a  given  amount  of  carbon  are  the  same  in  both  cases. 

When  both  CO  and  CO2  are  formed  in  and  carried  from  the 
producer,  the  equations  for  the  heat  balance  in  the  theoretical 
case  of  ico  per  cent  efficiency  have  the  forms: 

For  cubic  foot  units, 

328  H  =  132.500  +    462  CO2; 

for  pound  units, 

61,984  H  =  1803  CO  +  3995  C02, 

in  which  the  numerical  coefficients  are  heat  values  at  62°  F.  and 
14.7  pounds  per  square  inch  absolute  pressure. 

The  accuracy  of  the  above  equations  depends  on  the  correct- 
ness of  the  heat  values  used.  The  ones  here  adopted  seem  to 
have  been  determined  with  great  care. 

If  when  numerical  substitutions  and  computations  are  made 
for  these  equations  the  left-hand  member  in  either  is  greater 
than  the  right-hand  member,  it  is  an  indication  that  the  pro- 
ducer is  absorbing  more  heat  for  the  decomposition  of  water  than 
is  being  generated  by  the  combustion  of  carbon  in  the  producer. 
Such  a  condition  can  exist  temporarily  in  a  producer  that  does 
not  receive  heat  or  energy  from  outside  sources,  but  must  be 
paid  for  with  leaner  gas  during  a  consecutive  period  of  operation. 

The  above  equations  are  not  applicable  when  hydrocarbons 
are  present  in  the  fuel  or  in  the  gas  produced. 


FUELS  AND  GAS  MAKING  347 

228.  Comparative  Heat  Losses  for  Burning  C  to  CO  or  to  C02 
in    the  Air-and- Water- Gas   Process  When  the  Gas  Leaves  the 
Producer  at  a  High  Temperature.  —  It  was  shown  in  the  pre- 
ceding section  that  when  C  is  burned  to  CO  in  the  producer 
there  are  theoretically  5.026  pounds  of  gas,  whose  specific  heat 
is  .288  B.t.u.  per  pound,  generated  per  pound  of  C  burned  to  CO; 
and  that  when  the  C  is  burned  to  CO2  in  the  producer  there  are 
6.46  pounds  of  gas,  having  a  specific  heat  of  .345  B.t.u.  per  pound, 
generated  per  pound  of  C  burned  to  CO2. 

The  heat  required  for  raising  the  temperature  of  the  gas  i°  F. 
in  each  case  is : 

For  1  pound  C  burned  to  CO, 

5.026  X  .288  =  1.446  B.t.u., 
and  for  1  pound  C  burned  to  CO2 

6.46  X  .345  =  2.225  B.t.u. 

The  ratio  of  the  two  amounts  of  heat, 

2.225 

-,  =  1-54, 
1.446 

shows  that  when  in  the  air-and-water  gas  process  the  gas  leaves 
the  producer  at  a  higher  temperature  than  that  of  the  air,  water, 
and  fuel  used,  54  per  cent  more  heat  is  carried  from  the  producer 
by  the  gas  when  the  C  is  burned  to  CO2  than  when  it  is  burned 
to  CO.  This  numerical  value  applies  only  to  the  theoretical  case 
of  the  preceding  section,  and  also  assumes  that  the  specific 
heats  of  the  gases  produced  by  the  two  methods  of  burning 
retain  the  same  ratio  through  all  temperatures  up  to  that  at  which 
the  gas  leaves  the  producer.  The  latter  assumption  is  probably 
true  in  a  measure. 

The  heat  thus  carried  out  from  the  producer  is  mostly  lost 
during  the  cooling  of  the  gas  by  the  usual  methods.  It  is 
therefore  desirable  to  have  a  minimum  of  CO2  in  the  gas. 

229.  Fuels  for  Continuously  Operated  Suction  Producers.  - 
Since  the  continuously  operated  updraught  suction  producer  can- 
not be  opened  above  the  combustion  zone  for  stoking  or  other- 


348  THE  GAS  ENGINE 

wise  breaking  up  the  fuel,  on  account  of  air  being  drawn  in 
through  such  an  opening,  it  is  necessary  to  use  a  fuel  that  does  not 
cake  or  adhere  to  the  walls  of  the  combustion  space.  This  means 
that  the  fuel  must  be  practically  free  from  volatile  hydrocarbons. 
Mechanical  stoking  or  stirring  devices  that  enter  above  the  com- 
bustion zone  are  subject  to  detrimental  leaks. 

Hard  coal  (anthracite)  and  coke  are  therefore  the  only  fuels 
that  are  adapted  to  the  continuously  operated  suction  producer 
direct  connected  to  the  motor  after  the  manner  that  has  been 
described. 

230.  Pressure  Gas  Producers  for  Continuous  Operation.  - 
The  general  form  of  this  class  of  producer  is  much  the  same  as 
that  of  the  continuous  suction  producer.  The  draught  through 
the  producer  and  its  accessory  apparatus  is  caused  generally  by 
either  a  steam  jet  blower  that  forces  both  steam  and  air  into  the 
tightly  sealed  bottom  of  the  producer  or  by  a  mechanical  blower 
which  forces  the  air  in  while  steam  is  brought  in  separately.  In 
the  latter  case  the  steam  may  be  generated,  at  least  in  part,  in  a 
vaporizer  heated  by  the  gases  escaping  from  the  producer.  The 
steam  is  sometimes  taken  from  an  entirely  detached  steam- 
generating  plant. 

The  gas  passes,  in  the  more  usual  construction,  from  the 
producer  successively  through  a  vaporizer,  an  economizer  for 
heating  the  air  going  to  the  producer,  a  scrubber,  a  purifier,  and 
thence  to  a  storage  tank.  A  tar  extractor  is  sometimes  placed 
between  the  scrubber  and  the  purifier,  and  tar  drips  are  suitably 
located.  There  is  generally  one  between  the  economizer  and 
the  scrubber,  with  drainage  from  both.  Water  seals  are  used, 
through  which  the  gas  passes  on  its  way  to  storage,  but  cannot 
return.  The  seals  act  as  check  valves. 

The  fuel  can  be  stoked  through  openings  above  the  combustion 
zone  by  temporarily  reducing  the  blast  that  forces  the  air  through 
the  producer.  This  can  be  done  without  checking  the  operation 
of  the  motor,  since  the  storage  tank  will  supply  gas  during  a 
short  stoking  interval. 

The  charging  apparatus  is  made  so  that  fresh,  fuel  can  be 
charged  on  at  any  time  during  the  operation  of  the  producer. 


FUELS  AND  GAS  MAKING  349 

A  pair  of  small  doors  or  gates,  placed  in  series  after  the  manner 
of  those  in  an  air  lock,  are  used  for  charging  the  fuel  when  it  is 
done  by  hand.  Mechanical  chargers  have  suitable  provisions 
enabling  them  to  be  used  at  any  time. 

Caking  coals,  as  well  as  any  other  kinds,  can  be  used  in  the 
pressure  producer.  The  convenience  with  which  stoking  can  be 
done  by  hand  to  break  up  caked  coal  makes  it  entirely  practicable 
to  use  those  which  cake  to  the  highest  extent.  Mechanical 
stokers  or  stirrers  driven  from  above  the  combustion  space  for 
continuously  stirring  the  fuel  are  used  to  some  extent.  Leak- 
age and  rapid  deterioration  by  the  heat  are  serious  features  to  be 
dealt  with  in  the  use  of  a  mechanical  stoker  of  this  class. 

Various  methods  of  sealing  the  ash  pit  find  application.  Water 
is  very  commonly  used  for  the  seal.  Mechanical  sealing  is  also 
extensively  used. 

When  fuel  containing  volatile  hydrocarbons  is  used,  the 
volatile  part  is  distilled  off  and  passes  out  with  the  other  con- 
stituents of  the  gas.  Unless  care  is  taken  to  have  the  producer 
of  a  suitable  form,  and  to  operate  it  properly,  a  large  portion  of 
the  volatile  gas  will  be  of  such  a  nature  as  to  condense  at  or  above 
atmospheric  temperature  and  pressure,  that  is,  during  the 
cleaning  and  cooling  of  the  gas.  But  if  the  producer  has  ample 
and  properly  formed  space  above  the  fuel  bed  and  the  temperature 
is  kept  high,  part  of  the  hydrocarbons  that  are  distilled  off  from 
the  fuel  as  condensable  gases  (at  atmospheric  temperatures  and 
pressures)  will  be  dissociated  and  their  elements  will  recombine 
in  gases  that  are  permanent  under  the  ordinary  conditions  of 
utilization.  There  are  objections  to  keeping  the  temperature  of 
the  fuel  bed  very  high.  Some  of  these  objections  are  on  account 
of  the  increased  loss  of  heat  carried  away  by  the  gases,  and 
increased  fusing  and  clinkering  of  the  fusible  part  of  the  ash. 

The  government  tests  at  St.  Louis,  of  bituminous  coals  and 
lignites  in  an  up-draught,  pressure  producer  for  continuous 
operation  and  of  the  general  class  just  described,  gave  tar  in 
quantities  approximately  from  10  gallons  to  23  gallons  per  ton  of 
coal  used  in  the  producer.  The  volatile  matter  in  the  coal  varied 
from  about  21  to  40  per  cent  in  the  different  varieties.  The  tar 


350  THE  GAS  ENGINE 

from  the  bituminous  coals  was  black,  and  that  from  some  of  the 
lignites  was  of  a  brown  color. 

The  tar  is  practically  all  waste  in  such  cases,  and  is  disagree- 
able to  have  about  the  apparatus. 

The  aim  of  many  producers  using  bituminous  coals  and  lignites 
is  to  completely  break  up  the  condensable  hydrocarbons  so  that 
they  will  form  into  others  that  are  permanent  gases. 

Tar-burning  apparatus  for  burning  the  tar  under  steam 
boilers  is  used  in  connection  with  some  gas  power  plants.  The 
method  of  burning  is  similar  to  that  for  oil  fuels,  the  tar  being 
preheated  to  liquefy  it. 

231.  Down-Draught  Continuous  Gas  Producer.  —  If  coal  is 
charged  or  fed  on  at  the  top  of  the  fuel  bed  and  the  draught 
through  it  is  downward  from  the  top  to  the  ash  pit,  then  the 
volatile  gases  distilled  off  from  the  green  fuel  will  have  to  pass 
down  through  the  hot  zone  of  combustion  before  escaping  from 
the  producer.     By  this  process  the  heat  of  the  fuel  bed  dissociates 
the  condensable  hydrocarbons  and  converts  them  into  perma- 
nent gases  more  completely  than  when  the  draught  is  upward 
and  the  fuel  fed  on  at  the  top. 

In  practice  both  air  and  steam  are  blown  or  drawn  into  the 
upper  part  of  the  continuous  producer  and  the  gas  taken  out  from 
the  bottom.  Hand  stoking  for  breaking  up  the  caked  fuel  can 
be  done  readily  when  the  draught  is  produced  by  the  suction 
of  an  exhauster  connected  to  the  bottom  of  the  producer  for 
drawing  out  the  gas. 

232.  Under-Feed  Continuous  Gas  Producer.  —  Another  method 
of  causing  the  distilled  gases  to  pass  through  the  hot  bed  of  the 
fuel  before  leaving  the  producer,  is  to  feed  the  fuel  in  at  the  bottom 
of  the  producer  and  have  the  draught  through  the  fuel  from  the 
bottom  to  the  top.     Numerous  forms  of  this  class  of  producer 
have  been  used  more  or  less  extensively.     The  steam  and  air  may 
be  either  blown  in  or  drawn  in  by  suction,  entering  the  producer 
below  the  fuel  bed,  and  the  produced  gases  taken  out  at  the  top  of 
the  producer. 

233.  Air  and  Carbon  Dioxide  Continuous  Gas-Making  Process. 
—  It  has  been  pointed  out  that  when  simple  air  gas  is  made  there 


FUELS  AND  GAS  MAKING  351 

is  a  great  loss  of  heat  on  account  of  the  high  temperature  at  which 
gas  leaves  the  producer,  when  the  gas  is  cooled  before  using,  unless 
unusual  means  are  adopted  for  utilizing  its  sensible  heat.  The 
combined  air-  and  water-gas  processes  that  have  been  mentioned 
prevent  the  loss  of  heat  to  so  great  an  extent  on  account  of  keeping 
down  the  temperature  of  the  gas  by  utilizing  trie  surplus  heat  of 
combustion  to  some  extent  for  dissociating  the  water. 

A  method  of  keeping  down  the  temperature  of  the  fuel  and  of 
the  gas  without  the  use  of  water  or  steam  has  recently,  been 
devised  and  put  into  operation.  In  this  method  exhaust  gases 
from  the  combustion  motor  are  mixed  with  the  air  entering  the 
fuel  bed  in  the  producer.  Since  no  water  is  used  in  the  process, 
the  exhaust  gas  from  the  motor  contains  a  large  amount  of  CO2. 
The  CO2  upon  entering  the  fuel  bed  with  the  air  is  transformed 
into  CO  in  the  producer  by  dissociation,  during  which  part  of  the 
O  of  the  CO2  takes  up  C  from  the  fuel.  The  heat  absorbed  by 
the  dissociation  of  the  CO2  is  greater  than  that  liberated  by  the 
recombination  of  the  nascent  O  with  C,  so  that  the  net  result  is  a 
cooling  effect.  The  temperature  of  the  fuel  bed  is  kept  up  by  the 
air-burned  part  of  the  fuel.* 

The  plant  was  operated  on  both  anthracite  and  bituminous 
coal.  The  cooling  effect  of  the  water  vapor  from  the  motor 
exhaust  gas  when  hydrocarbons  are  present  in  considerable  quan- 
tity with  the  use  of  bituminous  coal,  is  not  taken  up  by  the 
inventor  of  the  process  in  his  description  of  it  as  referred  to. 

A  fuel  consumption  of  .7  of  a  pound  of  coal  per  horsepower 
per  hour  when  the  plant  operated  continuously  at  full  load  for 
24  hours  a  day  for  a  considerable  period  is  reported.  When 
operating  ten  hours  a  day  and  closing  down  Sundays  with  a  load 
factor  of  about  two-thirds,  the  fuel  per  horsepower  per  hour 
averaged  1J  pounds  of  coal. 

The  motor  was  of  the  four-cycle,  single-acting,  three-cylinder 
vertical  type  with  a  capacity  of  about  100  horsepower. 

234.  Combined  Pressure  and  Suction  Producer.  —  By  com- 
bining both  the  pressure  and  the  exhaust  methods  of  operating 
a  producer,  the  pressure  above  the  fuel  can  be  maintained  at  or 
*  Proceedings  Amer.  Soc.  Mech.  Engrs.,  June,  1908,  Vol.  30. 


352 


THE  GAS  ENGINE 


FUELS  AND   GAS  MAKING 


353 


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"cSSGoM  ^'C^TJ'^^-1^  "     4>     C  v» 

^  2^°.s      &?.fI-aAl^  ^':     -S  S 


354  THE   GAS  ENGINE 

very  slightly  above  atmospheric,  so  that  stoke  holes  can  be  opened 
into  the  gas  space  without  appreciable  escape  of  gas  while  the 
gasifying  process  is  under  way.  This  combination  is  found  in 
the  practical  field. 

235.  Miscellaneous  Types  of  Continuous  Gas  Producers  for 
Volatile  Coals.  —  There  are  numerous  types  of  continuous-acting 
gas  producers  intended  to  eliminate  the  tarry  products  from  the 
gas  generated  from  coals  containing  volatile  hydrocarbons.  In 
all  of  them  the  object  is  to  heat  the  distilled  gases  to  a  high  tem- 
perature before  they  leave  the  producer. 

A  quite  common  method  of  doing  this  when  the  coal  is  charged 
on  at  the  top  or  upper  part  of  the  producer  and  the  steam  and  air 
enter  from  the  bottom  or  from  the  ash  pit,  is  to  have  the  inner 
orifice  for  the  outlet  of  the  gas  from  the  producer  below  the  top 
level  of  the  fuel.  The  distilled  gases  then  fill  such  a  portion  of 
the  upper  part  of  the  chamber  above  the  zone  of  combustion  as 
is  not  occupied  by  fuel,  and  pass  down  through  the  incandescent 
fuel  to  the  orifice  of  the  outlet.  The  outlet  is  sometimes  a  water- 
jacketed  tube  or  pipe  extending  down  into  the  central  part  of  the 
fuel  bed  and  open  at  the  lower  end.  In  other  cases  there  are  a 
number  of  ports  in  the  wall  of  the  producer  below  the  top  level 
of  the  fuel. 

Air  and  steam  are  sometimes  admitted  at  both  the  top  and 
bottom  of  the  fuel  bed  and  the  gas  is  carried  out  through  ports 
well  below  the  top  level  of  the  fuel  bed  and  of  the  combustion 
zone. 

Another  method  of  highly  heating  the  distilled  gases  is  to  have 
a  secondary  fire  in  the  producer  so  located  that  the  gas  from  the 
main  fuel  bed  must  pass  through  the  secondary  fire  before 
escaping  from  the  producer.  The  secondary  fire  is  naturally  of 
a  non-volatile  fuel,  as  coke  or  anthracite  coal. 

Still  another  method  is  to  have  a  pipe  or  other  down-take 
passage  lead  from  the.  top  of  the  gasification  chamber  to  the  ash 
pit  so  that  the  distilled  gases  will  be  carried  down  and  enter  the 
bottom  of  the  fuel  bed  with  the  air  and  steam.  Some  means  of 
creating  a  down  draught,  as  a  steam  blower,  is  necessary  in  the 
down-take  passage. 


FUELS  AND  GAS  MAKING  355 

Two  producers  are  sometimes  used  in  conjunction  for  the  con- 
tinuous production  of  gas  from  bituminous  coal.  The  draught 
is  in  either  direction  in  the  first  one,  but  enters  the  fuel  bed  of  the 
other  at  the  green  or  fresh  fuel  side,  so  that  all  the  gases  from  the 
first  producer  and  all  the  distilled  gases  from  the  second  must 
pass  through  the  hot  combustion  zone  of  the  second  producer. 
Air  and  steam  are  added  to  the  gas  ,from  the  first  producer  before 
it  enters  the  fuel  of  the  second  one. 

236.  Intermittent  Gas-Making  Processes  in  General.  —  Instead 
of  carrying  out  the  combined  operations  of  burning  coal  with  air 
and  decomposing  steam  to  burn  more  of  the  carbon  and  liberate 
hydrogen,  the  two  processes  are  carried  on  separately  in  some 
cases. 

For  power  gas  purposes,  a  pair  of  producers  operating  in  con- 
junction are  generally  used  for  the  intermittent  process.  This 
is  not  always  the  method,  however. 

If  in  any  of  the  forms  of  producers  that  have  been  briefly 
discussed,  air  only  is  blown  or  drawn  through  the  fuel  at  a  rate 
as  great  as  compatible  with  gas-making  processes,  the  body  of  the 
fuel  will  soon  become  highly  heated.  Then,  after  it  has  attained 
a  sufficiently  high  temperature,  if  the  air  is  cut  off  and  steam 
blown  into  the  incandescent  fuel,  water  gas  will  be  formed  as 
long  as  the  fuel  remains  hot  enough  to  cause  the  necessary 
chemical  changes.  When  the  fuel  becomes  as  cool  as  allowable, 
turning  the  air  blast  on  again  after  cutting  off  the  steam  will 
reheat  the  fuel,  and  so  on. 

The  nature  of  the  gases  passing  off  during  the  blow  with  air 
depends  chiefly  on  the  compactness  and  thickness,  or  depth,  of 
the  fuel  bed  and  the  rate  of  blowing.  If  the  fuel  bed  is  deep  and 
compact,  the  resulting  gas  will  be  combustible  on  account  of 
containing  a  considerable  amount  of  CO  and  generally  very 
little  CO2.  But,  on  the  other  hand,  if  the  fuel  bed  is  thin  and 
open,  a  strong  blast  will  send  so  much  air  into  the  fuel  that  CO2 
will  be  the  principal  compound  of  C  and  O  formed,  and  the  gas 
will  not  be  combustible.  The  heating  of  the  fuel  bed  will  be 
much  more  rapid  when  CO2  is  formed  chiefly  than  when  a 
combustible  air  gas  is  produced. 


356  THE  GAS  ENGINE 

Both  the  above  methods  of  blowing  air  into  the  fuel  find  appli- 
cation in  intermittent  gas-making  processes.  Which  shall  be 
selected  depends  on  the  kind  of  gas  desired.  That  in  which 
combustible  gas  is  made  during  the  period  of  air  blowing  seems 
to  have  been  in  use  much  longer  and  finds  far  more  extensive 
application  than  that  in  which  non-combustible  gas  is  made 
during  the  period  of  blowing.  The  air  gas  and  water  gas  of  the 
latter  method  can  be  mixed  and  used  together  in  the  combustion 
motor  with  entirely  satisfactory  results. 

237.  Twin  Producers  for  Intermittent  Gas  Making.  —  Producers 
are  often  used  in  pairs,  the  main  object  in  pairing  them  being  to 
secure  the  secondary  fire  action  on  the  unstable  gases  that  are 
distilled  from  the  green  fuel.  A  third  producer  is  sometimes 
installed  as  a  relay  in  such  plants  when  there  is  a  practically 
continuous  demand  for  gas  —  no  shut  downs. 

•One  method  of  operating  the  twin  producers  on  bituminous 
coal  is  to  blow  both  (with  air  only)  from  the  top  in  parallel  so 
that  the  air  passes  down  through  the  fuel  that  is  charged  on  at 
the  top  and  the  non-stable  gases  of  distillation  are  broken  up 
into  stable  gases  (and  some  free  carbon  generally)  by  passing 
down  through  the  hot  zone  of  combustion.  The  blow  is  continued 
till  the  fuel  is  sufficiently  hot.  The  air  is  then  cut  off  and  the 
steam  admitted  into  the  sealed  space  below  the  fuel  in  one  of 
the  producers,  so  that  it  passes  up  through  the  fuel  in  one  of  the 
producers  and  then  over  to  the  top  of  the  other  producer,  and 
thence  down  through  the  second  fuel  bed.  All  the  gases  distilled 
during  the  "run"  with  steam  have  to  pass  through  the  incan- 
descent fuel  in  the  second  bed  and  are  there  acted  on  by  the  heat 
to  dissociate  and  convert  the  unstable  ones  into  permanent  gases. 
Air  is  then  blown  in  again  after  shutting  off  the  steam.  After 
sufficient  heating  the  air  is  cut  off  again  and  another  run  made 
with  steam,  but  this  time  the  steam  is  admitted  at  the  bottom  of 
the  other  producer,  so  that  the  path  of  the  water  gas  and  the 
distillates  that  accompany  it  is  reversed.  Air  blowing  then 
comes  again  and  the  whole  cycle  is  repeated. 

If  the  draught  of  air  during  the  blowing  period  fe  induced  by 
an  exhauster  interposed  in  the  gas  main  from  the  producer,  the 


FUELS  AND  GAS  MAKING 


357 


Hydraulic  Piston 


Steam  Valve 


Ash  pit      , 

DoorW^   Generate 

/\    ^ 


aning 


To  Exhauster  and  Producer 
~~*    Gas  Holder 


FIG.  116. 
Intermittent  Downdraught  Gas  Producer  Plant. 

Showing  contents  of  producer  after  51  hours'  run  at  practically  full  load  without 
shutdown  of  engine.  5oo-horsepower  engine. 

The  fresh  or  green  fuel  charge  was  made  up  largely  of  anthracite  with  a  topping  of 
bituminous  coal.  Bituminous  coal  was  charged  on  at  the  top  as  needed. 

The  producers  were  blasted  at  the  same  time  in  parallel  with  a  down  draft  of  air. 
Steam  was  blown  into  the  bottoms  of  the  producers  alternately  between  air- 
blasting  periods;  into  No.  i  after  the  first  period  of  air  blasting,  and  into  No.  2 
after  the  second  air  blast,  etc.  Proc.  Amer.  Soc.  Mech.  Engrs.,  mid-November, 
1997. 


358  THE   GAS  ENGINE 

producers  can  be  left  open  at  the  top  during  this  part  of  the 
operation  and  fuel  fed  in.  This  obviates  the  use  of  an  air  lock 
at  the  charging  door. 

It  can  doubtless  be  seen  that  there  are  several  other  methods 
of  working  producers  in  pairs  while  always  securing  the 
breaking  up  of  the  unstable  gases  by  passing  them  through  hot 
fuel. 

238.  Blast -Furnace  Gas.  —  The  blast  furnace  for  reducing 
iron  ore  to  pig  iron  discharges  combustible  gas  from  the  top  of 
the  burden  of  ore,  fuel,  and  flux  that  is  charged  into  it.  Air  only 
is  blown  in  through  the  tuyeres  near  the  bottom  of  the  enclosed 
chamber.  In  the  lower  part  of  the  burden  the  process  is  probably 
nearly  identical  with  that  for  making  air  gas.  As  the  air  gas 
made  in  the  lower  part  passes  upward  it  undergoes  various 
chemical  changes  of  which  the  net  result  is  the  addition  of  oxygen 
to  a  part  of  the  CO  that  started  up  from  the  lower  part  of  the 
furnace.  This  additional  oxygen  comes  from  the  ore  during  its 
reduction  from  an  oxide  of  iron  to  metallic  iron.  When  lime- 
stone, CaCOg,  is  used  for  the  flux,  CO2  is  driven  off  from  it  at  the 
upper  part  of  the  furnace  and  mingles  with  the  escaping  gas. 

CaC03  =  CaO  +  CO2. 

The  air  gas  that  was  formed  at  the  lower  part  of  the  furnace 
is  therefore  reduced  in  richness  (made  leaner)  as  it  passes  up 
through  the  furnace.  If  lime  is  used  as  a  flux,  there  is  less 
dilution  of  the  gas  than  with  limestone  as  the  flux.  If  the  fuel 
contains  volatile  hydrocarbons,  these  will  be  distilled  off  and  the 
gas  will  be  enriched  by  them. 

The  composition  of  blast-furnace  gas  varies  therefore  with  the 
kinds  of  fuel,  flux,  and  ore.  As  produced  in  the  general  method 
of  practice  of  iron-ore  reduction,  it  has  a  lower  heating  value  per 
cubic  foot  than  that  made  by  any  of  the  producer  methods  under 
proper  conditions  of  operation.  A  richer  gas  will  generally  come 
from  a  blast  furnace  using  coal  than  from  one  using  coke, 
the  increased  richness  being  due  to  the  volatile  portion  of  the 
coal. 


FUELS  AND  GAS  MAKING  359 

With  coke  as  a  fuel  in  the  blast  furnace  there  is  very  little 
hydrogen  in  the  gas,  since  the  moisture  in  the  air  and  the  charge 
is  then  the  chief  source  of  hydrogen.  It  has  been  pointed  out  by 
those  dealing  with  blast  furnaces  that  if  the  blast  carries  water 
in  from  a  slight  water  leak  at  a  tuyere,  there  will  be  a  very  material 
addition  of  hydrogen  to  the  gas  and  a  change  of  heat  value. 
The  gas  must  of  course  be  cleaned  so  as  to  be  free  from  dust 
and  grit  before  using  in  the  combustion  motor. 

239.  Coke-Oven  Gas.  —  In  the  manufacture  of  coke,  bitu- 
minous coal  is  heated  so  that  the  volatile  part  is  driven  off  almost 
completely.  The  remainder  is  the  coke  product  for  which  the 
operation  is  carried  on.  Coke  making  is  in  a  general  way  similar 
to  gas  making  by  the  retort  process  with  bituminous  coal.  The 
chief  product  in  one  case  is  the  by-product  in  the  other.  The 
chief  difference  in  the  two  processes  is  in  the  rate  of  gasification. 
In  gas  making  the  rate  of  distillation  is  such  as  to  secure  the  best 
results  in  the  gas  made;  in  coking  the  rate  is  regulated  to  procure 
the  best  coke,  which  is  generally  that  which  is  the  strongest 
for  resisting  mechanical  stress.  The  coals  for  the  two  proc- 
esses are  of  course  selected  with  a  view  to  the  best  results  in 
each  case. 

In  retort  processes  of  coking  coal  the  heat  is  supplied  by 
burning  the  gas  that  is  distilled  off.  With  a  fat  coal  there  is 
more  of  the  gas  than  is  needed  for  coking  when  the  coke  oven 
is  suitably  made.  This  excess  of  gas  can  be  used  in  the 
combustion  motor  successfully.  It  is  a  richer  gas  generally 
than  that  made  by  any  of  the  producer  processes  that  have 
been  mentioned.  Its  richness  varies  with  the  kind  of  coal 
and  the  stage  of  completion  of  the  distillation.  The  following 
is  taken  from  a  paper  on  "The  By-Product  Coke  Oven"  by 
Mr.  W.  H.  Blauvelt* 

"The  surplus  from  the  by-product  coke  oven  is  the  portion 
remaining  after  sufficient  gas  has  been  used  for  heating  the  ovens, 
and  the  amount  varies  greatly  with  the  fuel  used.  In  lean  coals, 
low  in  volatile  matter,  there  might  perhaps  be  no  surplus,  while 
in  rich  gassy  coals  the  amount  may  be  from  4000  to  4500  feet  per 
*  Proceedings  Amer.  Soc.  Mech.  Engrs.,  March,  1908,  Vol.  30. 


360  THE  GAS  ENGINE 

net  ton  of  coal.     ...  the  gas  is  essentially  similar  to  that  made 
in  gas  works.     Following  is  a  typical  analysis: 

Carbon  dioxide 1.3 

Benzene 1.2 

Ethylene 4.2 

Oxygen 0.5 

Carbon  monoxide 5.1 

Methane 35.5 

Hydrogen 48 .  o 

Nitrogen 4.2 

B.t.u.  per  cubic  foot 679 

"The  calorific  value  of  the  gas  may  vary  from  550  to  750  B.t.u. 
per  cubic  foot. " 

240.  Oil  Gas  from  Petroleum.  —  When  petroleum  is  destruc- 
tively distilled  by  bringing  small  quantities  at  a  time  in  contact 
with   red-hot  substances,  the  heavy  hydrocarbons  are  changed 
into  others  which  are  mostly  permanent  gases  under  atmospheric 
conditions.     The  gas  varies  in  composition  with  the  temperature 
of  distilling  and  the  fineness  of  division  of  the  liquid  when  it 
comes  into  contact  with  the  hot  surface.     In  a  general  way  the 
oil  gas  made  in  this  manner  resembles  coal  gas  by  the  retort 
process.     Oil-water  gas  is  also  made  from  petroleum  by  mixing 
steam  with  the  vaporized  oil. 

Oil  gas  is  too  expensive  for  economical  use  in  the  combustion 
motor. 

241.  Gasoline  Gas  or  Carbureted  Air.  —  If  air  is  caused  to 
bubble  through  gasoline,  or  is  brought  into  contact  with  fabrics, 
wire  gauze,  etc.,  that  are  saturated  with  gasoline,  it  will  become 
impregnated  with  the  vapor  of  gasoline  to  an  extent  that  depends 
on  the  time  and  intimacy  of  contact  of  the  air  with  the  gasoline. 
If  the  amount  of  gasoline  taken  up  does  not  exceed  two  gallons 
per  1000  cubic  feet  of  air,  the  gasoline  vapor  will  remain  a  vapor 
in  the  air  under  atmospheric  conditions. 

Gas  made  in  this  manner  can  be  used  in  the  internal-combustion 
motor  and  for  illuminating.  The  gas  must  be  mixed  with  air  for 
burning  in  the  motor,  after  the  manner  of  other  gases. 


FUELS  AND  GAS  MAKING  361 

242.  Tar  Destruction  in  Gas  Making.  —  Some  .of  the  methods 
of  tar  destruction  by  passing  the  unstable  gases  from  coal  and 
lignites  through  carbon  or  fuel  heated  to  incandescence  have 
been  mentioned  in  connection  with  different  processes  of  gas 
making.     The  destruction  of  the  tar  is  practically  complete  by 
at  least  part  of  these  methods  when  the  apparatus  is  properly 
operated. 

There  is  generally  a  formation  of  free  carbon  in  a  granular  or 
graphitic  state  accompanying  the  destruction  of  tar  vapors  in 
this  manner.  The  gas-making  plant  must  therefore  be  designed 
with  provision  for  cleaning  the  carbon  deposit  from  such  places 
as  it  may  lodge,  and  for  removing  the  carbon  from  the  gas.  The 
graphitic  carbon  does  not  wash  out  in  the  ordinary  coke  or  other 
types  of  scrubber  as  well  or  completely  as  the  carbon  that  comes 
from  a  producer  that  has  no  special  provision  for  tar  destruction 
and  which  allows  most  of  the  heavy  hydrocarbons  to  pass  out  as 
condensable  gases  that  form  tar. 

The  graphitic  carbon  can  be  filtered  out  by  passing  the  gas 
through  excelsior,  cloth,  burlap,  etc.,  which  should  not  be  so 
closely  woven  or  packed  as  to  prevent  reasonably  free  flow  of  the 
gas  through  it.  This  method  is  similar  to  that  used  sometimes 
for  cleaning  air  for  ventilation. 

243.  Variation    in    Quality    of    Producer    Gas.  —  There    are 
several  causes  that  make  considerable  variation  in  the  quality  or 
heating  power  of  the  gas  from  a  producer. 

It  has  already  been  pointed  out  that  temporary  increase  of 
the  steam  or  water  supplied  to  a  continuous  producer  will  give  a 
temporarily  richer  gas  than  the  producer  can  regularly  supply. 
Cutting  down  the  steam  temporarily  or  continuously  will  give  a 
leaner  gas. 

Cracks  in  the  bed  of  fuel,  or  settling  of  the  fuel  away  from 
the  walls  of  the  producer  when  bituminous  coal  is  used,  tends  to 
let  the  air  and  steam  pass  through  without  undergoing  the 
required  chemical  changes.  Generally  more  than  the  normal 
amount  of  CO2  and  a  lean  gas  result.  This  trouble  can  be 
obviated  by  proper  attention  to  stoking  and  charging  of  the  fuel. 

Variation  in  the  thickness  of  the  fuel  bed,  as  by  the  bed  becom- 


362  THE  GAS  ENGINE 

ing  thin  by  the  accumulation  of  ash  while  the  top  level  is  kept  at 
a  constant  height,'  also  affects  the  quality  of  the  gas. 

The  chemical  changes  are  not  the  same  in  their  ultimate  results 
when  the  temperature  of  the  fuel  is  low  as  when  it  is  high.  Dif- 
ferent qualities  of  gas  result  under  the  two  conditions.  The 
nature  of  the  variation  with  the  change  of  temperature  depends 
so  much  on  the  condition  and  kind  of  fuel,  the  thickness  of  the 
fuel  bed,  and  the  force  of  the  blast,  that  it  is  hardly  possible  to 
make  general  statements  regarding  them. 

244.  Observation  of  Quality  of  Gas  from  a  Producer.  —  When 
operating  a  gas  producer  in  regular  service,  it  is  desirable  to 
know  practically  all  the  time  the  quality  or  heating  value  of  the 
gas  flowing  from  the  producer,  and  essential  to  know  it  at  frequent 
intervals.  Some  means  that  indicate  the  quality  of  the  gas 
within  a  few  seconds  at  most  after  it  has  passed  from  the  producer 
is  necessary  for  the  best  operation.  Promptness  in  indicating 
the  quality  is  of  more  importance  than  accuracy  of  the  results 
except  when  efficiency  tests  of  the  producer  or  motor  are  being 
made. 

An  open  flame  of  the  gas  is  a  fair  indication  to  the  trained 
eye  of  its  nature.  The  gas  burner  can  be  attached  to  the 
gas  main  leading  from  the  scrubber.  If  the  gas  is  led  to  the 
burner  through  a  glass  tube  stuffed  with  absorbent  cotton,  the 
condition  of  the  cleanliness  of  the  gas  can  be  observed. 

Since  most  producer  gas  burns  with  a  non-luminous  flame,  the 
quality  can  often  be  observed  more  accurately  by  the  use  of  an 
incandescent  mantle  on  the  burner,  or  some  other  device  which 
immediately  shows  change  of  temperature  to  the  eye.  The 
pressure  of  the  gas  going  to  the  burner  must  be  kept  constant  for 
such  a  burner. 

The  pressure  of  the  gas  at  the  burner  can  be  kept  constant  by 
the  use  of  a  simple  and  inexpensive  aspirator  or  other  device  for 
drawing  it  continuously  from  the  mains  and  delivering  it  to  the 
burner  at  constant  pressure. 

If  the  incandescent  test  burner  is  placed  near  a  light  of  uniform 
strength,  a  still  more  accurate  means  is  arrived  at'for  noting  the 
quality  of  the  gas.  A  simple  photometric  device  for  comparing 


FUELS  AND   GAS  MAKING  363 

the  degree  of  luminosity  of  the  incandescent  pa/ts  obviates  the 
error  incident  to  direct  observation  of  the  lights. 

The  temperature  of  the  products  of  combustion  when  some  of 
the  producer  gas  is  burned  in  an  open  flue  is  a  prompt  method 
of  determining  the  quality  of  the  gas  for  the  purpose  of  managing 
a  producer. 

The  temperature  of  the  gases  leaving  the  producer  is  also  an 
indication  of  how  the  producer  is  working.  It  can  be  taken 
with  a  thermometer  inserted  in  the  gas  main,  which  may  be 
arranged  to  read  at  a  distance  in  a  suitable  location. 

245.  Continuous  Calorimeter  Tests  of  Gas  from  Producer.  — 
More  refined  tests  of  the  quality  of  the  gas  within  a  short  time  after 
it  leaves  the  producer  can  be  made  by  suitable  types  of  calo- 
rimeters. Several  instruments  for  this  purpose  have  been  devised 
and  operated.  The  principle  of  operation  is  generally  that  of 
feeding  the  calorimeter  both  gas  and  water  in  predetermined 
rates  and  observing  the  change  of  temperature  of  the  water  while 
flowing  through  the  calorimeter.  The  most  common  method 
seems  to  be  to  keep  a  constant  ratio  between  the  water  passed 
through  the  calorimeter  and  the  Amount  of  gas  consumed  in  the 
same  instrument. 

The  gas  for  the  calorimeter  is  generally  drawn  continuously 
at  a  constant  rate  from  the  gas  main  of  the  producer  at  a  suitable 
point.  The  calorimeter  will  therefore  show  the  average  heat 
value  of  the  gas  only  when  the  rate  of  flow  from  the  producer 
is  uniform.  If  there  is  any  variation  in  the  rate  at  which  the 
producer  makes  gas,  the  mean  value  of  observations  of  the  calorim- 
eter taken  at  equal  time  intervals,  or  a  continuous  record,  will 
not  give  the  average  heat  value  of  the  gas  that  is  stored  in  a 
tank  during  the  operation  of  the  producer  for  any  period  of  time. 
There  is  generally  considerable  variation  in  both  the  quality  of 
the  gas  and  the  rate  of  its  production  even  in  continuous  types  of 
producers. 

For  accurate  results  in  the  use  of  a  continuous  calorimeter  of 
the  kind  just  mentioned,  the  gas  should  be  drawn  from  the 
producer  main  at  a  rate  proportional  to  the  rate  at  which  the  gas 
flows  through  the  main;  in  other  words,  at  a  rate  proportional 


364  THE   GAS  ENGINE 

to  the  rate  at  which  the  producer  is  making  gas  of  a  standard 
temperature  and  pressure.  Since  it  would  be  difficult  to  burn 
the  gas  in  the  calorimeter  at  a  greatly  different  and  rapidly 
varying  rate,  another  method  is  to  give  each  reading  of  the  calorim- 
eter a  weight  in  averaging  that  is  proportional  to  the  rate  of 
gas  production  at  the  instant  the  gas  corresponding  to  the  reading 
was  taken  from  the  main,  or  to  move  a  recording  chart  at  a  rate 
similarly  proportional  to  the  rate  of  making  the  gas.  There 
would  generally  be  difficulty  in  getting  accurate  records  in  the 
latter  manner,  however,  on  account  of  the  lag  of  the  calorimeter 
in  indicating  the  quality  of  the  gas. 

The  nature  and  extent  of  the  error  introduced  in  determining 
the  average  heat  value  of  gas  flowing  through  a  main  by  the  use 
of  the  method  of  taking  samples  of  gas  from  the  main  at  equal 
time  intervals  and  giving  each  determination  equal  weight  in 
averaging  is  shown  by  the  following  numerical  example. 

A  combustion  motor  delivering  mechanical  power  at  a  constant 
rate  requires  2,000,000  B.t.u.  of  gas  per  hour.  The  gas  varies  in 
lower  (effective)  heat  value  from  100  to  125  B.t.u.  per  cubic  foot 
of,  standard  gas.  When  the  gas  is  of  the  100  B.t.u.  quality,  the 
motor  will  take  20,000  cubic  feet  per  hour;  and  when  it  is  of 
the  125  B.t.u.  quality,  16,000  cubic  feet  per  hour  will  be  con- 
sumed. The  required  volume  of  the  leaner  gas  is  25  per  cent 
greater  than  that  of  the  richer  gas. 

If  the  motor  runs  on  each  kind  of  gas  an  hour,  the  average 
heat  value  of  the  total  amount  of  gas  used,  taking  volumes  into 
account,  which  is  the  correct  method,  is 

20.000  X  zoo  -f  16,000  X  125  r, 

— ^  =  in  B.t.u.  per  cu.  ft. 
36,000 

The  incorrect  average  heat  value,  as  found  by  giving  each 
determination  (100  and  125  B.t.u.)  equal  weight,  is 

100  +  "S  =  112.5  B.t.u.  per  cu.  ft. 

The  difference  of  the  two  heat  values  thus  obtained  is  1.5 
B.t.u.  The  incorrect  method  gives  a  value  ij  pef  cent  greater 
than  the  true  average  heat  value. 


FUELS  AND   GAS  MAKING  365 

The  same  amount  of  error  occurs  when  the  readings  of  a  con- 
tinuous calorimeter  that  takes  gas  from  a  main  at  uniform  rate 
are  used  without  correction  for  the  different  rates  of  flow  of  the 
lean  and  rich  gas  through  the  main. 

The  error  just  pointed  out  is  favorable  to  the  producer  and 
against  the  motor. 

Variations  in  the  heat  value  of  producer  gas  as  great  as  those 
that  have  been  used  in  this  example,  and  even  greater,  are  not 
unusual  in  practice. 

246.  Efficiency  Bases  of  Gas  Producers.  —  The  efficiency  of 
the  gas  producer  that  is  of  interest  to  the  manufacturer  and 
consumer  of  gas  for  the  internal-combustion  motor  is  the  ratio 
of  the  heat  value  of  all  the  gas  produced  from  a  stated  amount  of 
fuel  to  the  heat  value  of  all  the  fuel  and  all  the  mechanical  or 
electrical  energy  used  for  all  purposes  relative  to  the  production 
of  the  gas.  The  rate  of  gasification  is  also  of  importance,  since 
the  higher  the  rate  the  less  the  initial  cost  of  a  gas  plant  of  a  given 
capacity. 

It  is  an  open  question  whether  the  higher  or  the  lower  heat 
value  of  the  gas  shall  be  taken  in  determining  the  efficiency  of 
a  gas  producer.  It  should  therefore  be  distinctly  stated  which 
heat  value  is  to  be  used  in  any  guaranty  of  efficiency. 

Instead  of  expressing  the  effectiveness  of  the  action  of  the 
producer  as  efficiency,  a  convenient  and  suitable  method  is  to  state 
the  amount  of  gas  at  a  standard  temperature  and  pressure,  and 
the  heat  value  (higher  or  lower)  per  unit  volume  (as  a  cubic  foot) 
that  a  producer  and  its  accessories  will  deliver  from  a  stated 
weight  of  coal  or  other  fuel  of  a  stated  quality  (heat  value  per 
pound,  from  a  specified  mine  and  how  prepared,  etc.),  also  taking 
into  account  the  mechanical,  electrical,  or  other  energy  received 
from  outside  sources. 

In  both  the  above  cases  the  loss  of  unburned  fuel  in  the  ash 
counts  against  the  producer. 

On  account  of  the  loss  of  unburned  fuel  in  the  ash,  the  efficiency 
is,  for  some  purposes,  divided  into  grate  efficiency  and  efficiency 
of  such  other  parts  of  the  process  as  are  under  consideration. 
The  product  obtained  by  multiplying  together  the  grate  efficiency 


366  THE  GAS  ENGINE 

and  the  efficiency  of  the  other  parts  of  the  process  under  consider- 
ation is  the  real  efficiency  of  such  parts  of  the  process. 

The  expressions  for  the  commercial  efficiency  and  the  grate 
efficiency  of  a  gas  producer  are: 

Commercial ) B.t.u.  of  total  gas  made. 

efficiency  $       B.t.u.  of  fuel  fed  to  producer  +  B.t.u.  equivalent  of 
energy  received  by  producer  from  outside  sources. 

B.t.u.  of  fuel  actually  burned  in  producer. 

Grate  efficiency  = 

B.t.u.  of  fuel  fed  to  producer. 

For  other  efficiencies  the  items  included  depend  so  much  on 
the  kind  of  producer  and  the  methods  of  operating  the  auxiliaries 
that  it  is  hardly  possible  to  give  formulas  that  will  cover  more 
than  one  type  of  producer  and  its  accessories.  Outside  of  the 
commercial  efficiency  and  the  grate  efficiency  it  is  practically 
always  necessary  to  define  the  efficiency  by  the  items  included 
rather  than  by  a  specific  name. 

The  comparison  of  different  steps  of  the  process  in  producers 
similarly  operated  with  regard  to  the  method  of  producing  draught 
is  not  generally  difficult.  But  in  some  cases,  as  when  the  draught 
is  induced  by  mechanical  means  in  one  producer,  and  by  a  steam 
blower  in  the  other,  the  refinements  necessary  to  compare  effi- 
ciencies that  exclude  the  energy  for  inducing  the  draught  become 
such  as  to  necessitate  the  greatest  care  and  judgment  in  deter- 
mining the  required  data  by  trial. 

In  the  case  of  a  gas  power  plant  producing  its  own  gas,  the 
total  efficiency  of  the  conversion  of  the  heat  energy  of  the  coal 
into  mechanical  energy  delivered  by  the  motor  is  determined 
more  frequently  than  the  efficiency  of  the  producer  alone.  The 
reason  for  this  is  that  there  are  seldom  adequate  means  'for 
measuring  the  amount  of  gas  produced.  Gas  meters  of  sufficient 
capacity  are  cumbersome  and  expensive,  and  less  expensive 
means  are  not  sufficiently  accurate  for  reliable  results  under 
ordinary  circumstances. 


CHAPTER  XIX. 
PRESSURE-VOLUME  DIAGRAMS. 

247.  Equations  for  Work.  —  When  the  pressure  of  a  gas  or 
liquid  acts  on  a  piston  and  moves  it  with  a  rectilinear  motion, 
then,  if  the  piston  face  acted  on  by  the  pressure  is  flat  and  per- 
pendicular to  the  direction  of  its  motion,  the  energy  expended, 
or  work  dqne  in  moving  the  piston,  is  expressed  by  the  equation 

W=  pAL, 
in  which 

p=  pressure  per  unit  area, 

A  —  area  of  piston  face, 

L  =  length  of  stroke  of  piston. 

When  the  piston  face  does  not  lie  in  a  plane  perpendicular  to 
the  direction  of  its  motion,  as  when  the  face  is  crowned,  convex, 
irregular,  or  slanted,  then  A  can  be  taken  as  the  area  of  the  cross- 
section  of  the  space  through  which  the  piston  moves,  the  cross - 
section  being  perpendicular  to  the  direction  of  motion  of  the 
piston. 

In  the  equation  just  written,  the  product  of 

A  X  L  =  volume  swept  through  by  face  of  piston. 
The  equation  for  the  energy  expended  can  therefore  be  written 

ir->, 

in  which 

v  =  volume  swept  through  by  face  of  piston, 

and  the  other  notation  is  as  given  for  the  preceding  equation. 

If  the  piston  moves  against  (toward)  the  resistance  of  the 
pressure  on  its  face,  then  the  energy  delivered  to  the  gas  or  liquid 
by  the  piston  is  expressed  by  the  same  equations. 

367 


368  THE   GAS  ENGINE 

The  expression  W=  pv  can   be  represented  graphically  on  a 
diagram  with  rectangular  coordinates.     This  is  done  in  Fig.  117. 
Pressures  are  measured  from  the  horizontal  axis  OF  in  a  direc- 
tion perpendicular  to  OF.  Volumes 
are    measured    from    the    vertical 
axis  OP  in  a  direction  perpendic- 
ular to  OP. 

When  the  pressure  is  constant, 
as  has  been  assumed,  it  is  repre- 
sented throughout  the  stroke  of  the 
piston  by  the  horizontal  line  at  a 
distance  Op  from  the  F  axis.  The 


Area  = 


volume  swept  through  by  the  face  FIG.  117. 

of  the  piston  is  represented  by  the 

distance  Ov.  The  product  Op  X  Ov  is  therefore  represented  by 
the  area  of  the  rectangle  bounded  by  the  coordinate  axes  OP 
and  OF  together  with  the  lines  drawn  through  p  and  v  to  com- 
plete the  rectangle.  Instead  of  taking  Op  and  Ov  as  the  nota- 
tion to  indicate  corresponding  distances,  it  is  customary  to  use 
only  p  and  v  for  this  purpose.  By  this  notation 

pv  =  area  of  rectangle. 

The  area  of  the  rectangle  represents,  in  accordance  with  the 
scales  of  pressure  and  volume  selected,  the  energy  transferred 
from  the  gas  or  liquid  to  the  piston,  or  vice  versa. 

If  the  pressure  is  variable  during  the  stroke  of  the  piston,  as 
indicated  by  the  curved  line  in  Fig.  118,  then  the  area  enclosed 
by  the  curved  pressure  line,  the  coordinate  axes,  and  the  vertical 
through  V  can  be  determined  approximately  by  dividing  it  into 
several  vertical  strips  or  partial  areas  by  lines  parallel  to  the 
vertical  coordinate  axis,  then  multiplying  the  width  of  each  strip 
by  its  average,  or  mean,  height,  and  adding  all  the  products 
together.  The  mean  height  of  each  strip  must  be  determined 
by  judgment,  and  is  therefore  not  mathematically  accurate. 
The  sum  of  the  partial  areas  determined  as  stated  is  therefore 
the  approximate  area  of  the  total  enclosed  space. 

The  area  thus  determined  for  each  small  strip  approximately 


PRESSURE-VOLUME  DIAGRAMS 


369 


represents  the  work  done  while  the  piston  is  sweeping  through  a 
volume  corresponding  to  the  width  of  the  strip.  If  the  width  of 
the  first  strip  is  AXF,  and  its  mean  height  is  Pv  then  the  work  done 
while  the  piston  sweeps  through  the  volume  AtF  is  wl  =  P^F. 
And  similarly  for  the  second  partial  area,  w2  =  P2A2F.  And  so 
on  for  all  the  partial  areas. 


FIG.  118. 

The  total  work  done  during  the  complete  stroke  of  the  piston 
is  therefore  approximately 


W 


+  P2A2F  + 


+  .    .  +  PmAm7. 


If  all  the  partial  areas  are  of  the  same  width,  so  that  AXF  =  A2F 
=  A3F,  etc.,  the  mean  value  of  the  pressure  can  be  found  by  adding 
together  all  the  P's  and  dividing  their  sum  by  the  number  of 
partial  areas.  The  total  area  is  then  found  by  multiplying  the 
volume  V  by  the  mean  value  of  the  pressure,  thus, 


W  =  total  area  =  Pmean  V. 


When  the  partial  areas  into  which  the  total  area  is  divided 
become  almost  infinitely  great  in  number,  then  the  method  of 
determining  the  total  area  becomes  that  of  integral  calculus.  The 
width  of  each  strip  is  then  represented  by  the  differential  quantity 


370 


THE   GAS  ENGINE 


dV,  and  the  height  of  each  strip  is  represented  by  p,  as  in  Fig. 
1-19.  The  area  of  each  differential  strip  is  therefore  pdV.  The 
value  of  p  is  in  general  different  for  each  elementary  strip.  The 
work  or  mechanical  energy  corresponding  to  each  differential 
strip  can  be  called  dW.  The  equation  for  the  differential 
quantities  is  then 

dW  =  pdV. 

The  accurate  total  area,  or  work,  is  represented  by  the  integral 
of  the  differential  areas,  thus, 

W  =  total  area  = 

This  integration  can  be  performed  mathematically  only  when 
there  is  a  definite  known  relation  between  p  and  V.  In  general 
there  is  no  such  relation,  so  the  mathematical  integration  is  in 
general  impossible. 

The  planimeter  can  always  be  used  to  make  the  integration 
mechanically. 


FIG.  119. 

Fig.  119  shows  in  a  general  way  the  nature  of  the  variation  of 
the  pressure  when  gas  compressed  in  a  closed  cylinder  to  the 
volume  F!  is  allowed  to  expand  and  drive  out  a  piston  until  the 
volume  becomes  Vr  The  work  or  energy  transferred  from  the  gas 
to  the  piston  is  here  represented  by  the  area  bounded  by  the 


lines 
is 


PRESSURE-VOLUME  DIAGRAMS  371 

^     The  calculus  expression  for  ttye  work  or  area 

f*V 

W  =  total  area  =  /     pdV. 


If  the  piston  compresses  the  gas  from  the  volume  F2  to  Vv  the 
energy  that  the  piston  delivers  to  the  gas  is  represented  by  the 


FIG.  120. 

248.  Pressure-Volume  Diagram  for  Complete  Cycle.  —  Fig. 
1 20  represents  in  a  general  way  the  events  in  a  combustion  motor 
from  the  time  the  charge  of  combustible  mixture  is  received  in  the 
motor  cylinder  till  the  charge  has  been  compressed,  burned, 
expanded,  and  discharged  so  that  the  pressure  in  the  cylinder  is 
again  the  same  as  at  first  and  the  piston  has  returned  to  its  initial 
position.  In  this  case  the  horizontal  axis  OV  represents  zero 
pressure  (about  14.7  pounds  per  square  inch  below  atmospheric 
pressure). 

The  charge  at  the  initial  position  of  the  piston  has  the  volume 
Va  and  the  pressure  Pa  at  the  point  A  on  the  diagram.  During 
the  instroke  of  the  piston  the  charge  is  compressed  to  the  volume 
Vb  and  the  pressures  during  compression  are  represented  by  the 
line  AB.  After  the  completion  of  compression  the  pressure  is 
increased  from  Pb  to  Pc  by  the  partial  combustion  of  the  charge, 


372  THE   GAS  ENGINE 

while  the  volume  remains  unchanged.  The  volume  then  increases 
during  the  outstroke  of  the  piston  from  Vb  to  the  initial  value  Va. 
The  pressure  line  during  the  expansion  is  CD.  The  pressure 
then  falls  from  Pd  to  the  initial  pressure  Pa,  while  the  volume 
remains  constant. 

The  energy  delivered  to  the  gas  by  the  piston  during  com- 
pression is  represented  by  the  area  AVaVbBA;  and  the  energy 
delivered  to  the  piston  by  the  gas  during  the  outstroke  is  repre- 
sented by  the  area  CDVaVbC.  The  difference  of  these  two  areas, 
which  is  the  area  A  BCD  A,  represents  the  energy  received  by 
the  piston  during  the  complete  cycle.  No  mechanical  energy  is 
received  or  delivered  by  the  piston  during  the  changes  of  pressure 
at  constant  volume  from  B  to  C  and  from  D  to  A. 

The  diagram  A  BCD  is  the  pressure-volume  diagram  of  the 
motor  during  the  cycle.  Its  area  can  be  found  by  the  methods 
given  above.  The  calculus  expression  of  its  area  and  of  the 
energy  transferred  is 

W  =  area  ABCD  =  f  F*  hdV, 

JVb 

in  which  h  is  the  height  of  any  differential  vertical  strip  of  the 
area  enclosed  by  the.  lines  of  the  diagram  and  is  in  general  a 
variable.  The  value  of  h  for  any  differential  strip  is  equal  to 
the  difference  of  the  pressures  acting  on  the  piston  while  it 
occupies  the  two  corresponding  positions  on  the  instroke  and  on 
the  outstroke. 

When  the  area  of  the  diagram  has  been  determined  with  a 
planimeter,  the  mean  value  of  h  is  found  by  dividing  the  area  by 
the  horizontal  length  of  the  diagram  =  VaVb.  The  mathematical 
expression  is 

A  BCD  area  ABCD 


length  of  diagram         Va  —  Vb 
or 

Mean  effective  _  ,,         _         _  Area  of  diagram.  _ 
pressure  Length  of  diagram  X  Ibs.  per  sq.  in.  per 

inch  compression  of  indicator  spring 

which  is  the  mean  effective  pressure  of  the  diagram. 


PRESSURE-VOLUME  DIAGRAMS  373 

249.  Indicator  Diagram.  —  The  indicator  diagram  is  essen- 
tially a  pressure-volume  diagram,  generally  on  a  miniature  scale. 
The  fact  that  the  horizontal  length  represents  volumes  is  seldom 
taken  into  consideration,  however,  in  determining  indicated 
power  by  its  aid.  In  this  connection  its  use  is  to  give  the  mean 
effective  pressure.  The  latter  is  generally  determined  from  it 
either  by  the  aid  of  a  planimeter  for  finding  its  area,  and  then 
dividing  the  area  by  the  length  of  the  diagram,  or  by  the  use  of 
an  averaging  instrument  that  gives  a  direct  reading  of  the  mean 
height  of  the  diagram  after  its  tracing  point  has  been  passed 
around  its  profile  in  a  proper  manner. 

The  mean  effective  pressure  thus  determined  is  then  used  in 
connection  with  the  proper  factors  for  determining  horsepower, 
etc. 

Mechanical  integrators  which,  when  set  to  correspond  to  the 
piston  area,  length  of  stroke,  and  speed  of  rotation  of  the  motor 
from  which  the  indicator  card  was  taken,  give  a  direct  reading  of 
the  horsepower,  are  also  used. 


CHAPTER  XX. 
THEORETICAL  HEAT   CYCLES. 

250.  Assumptions  for  Theoretical  Cycles.  —  By  the  assump- 
tion  of  conditions  that  differ  more  or  less  from  those  under 
which  an  internal-combustion  motor  actually  operates,  it  becomes 
possible  to  obtain  theoretical  pressure-volume  diagrams  whose 
boundary  lines   represent   mathematical   equations   and   whose 
areas  can  be  determined  by  mathematical  integration.     Such 
diagrams  are  useful  in  pointing  out  in  a  general  way  the  features 
essential  to  securing  the  greatest  efficiency  in  actual  practice  for 
the  kind  of  cycle  under  consideration,  and  the  kind  of  cycle  that 
will  give  the  greatest  theoretical  efficiency  with  a  perfect  gas. 

Among  the  assumptions  to  be  made  from  the  theoretical  cases 
there  are  three  that  are  common  to  all  the  theoretical  cycles. 
They  are: 

First.   That  the  piston  moves  without  frictional  resistance. 

Second.  That  the  walls  of  the  space  in  which  the  gas  is  enclosed 
during  the  cycle  are  impervious  to  heat;  or  expressed 
otherwise,  that  the  motor  piston,  cylinder,  etc., 
neither  abstract  heat  from  the  gas  nor  give  up  heat 
to  the  gas. 

Third.   That  a  perfect  gas  is  used. 

251.  Notation.  - 

Cp  =  specific  heat  of  constant  pressure,  B.t.u.  per  pound. 
Cv  =  specific  heat  of  constant  volume,  B.t.u.  per  pound. 

G   =  j  =  factor    for   converting    foot-pounds     into     B.t.u.; 

GW=  B.t.u. 
H  =  total  heat  added  to  or  abstracted  from  the  gas,  B.t.u. 

374 


THEORETICAL  HEAT  CYCLES  375 

Hi  =  heat  input  by  combustion,  B.t.u. 
Hd  =  heat  discharged  or  discarded,  B.t.u. 
J  =  mechanical    equivalent    of    heat.     /  =  778    ft.-lbs.  = 

1  B.t.u. 

P   =  absolute  pressure,  pounds  per  square  foot  =  144  X  Ibs. 
per  sq.  in. 

P  V       P  V 

R    =     — Q — °  =  — * — i-  =  mechanical  work  done  by  the  expan- 

^0  *I 

sion  of  unit  weight  or  mass  of  a  perfect  gas  at  constant 

pressure  while  heat  is  added  to  increase  its  temperature 

one  degree.     Foot-pounds  per  Fahrenheit  degree  for  one 

pound  of  gas. 
S   =  sensible  heat  added  to  or  taken  from  a  gas  to  cause  change 

of  temperature.     Sensible  heat  is  that  which  affects  the 

thermometer.     B.t.u.  per  pound. 
T  =  absolute   temperature,   Fahrenheit   degrees.      The  zero 

of  absolute  Fahrenheit  temperature  is  459°  below  zero 

Fahrenheit,  which  is  491°  F.  below  the  freezing  point  of 

water  at  atmospheric  temperature. 
V  =  volume,  cubic  feet. 
W  =  mechanical  work,  foot-pounds. 
/?    =  ratio  of  specific  volume  of  products  of  combustion  to 

specific  volume  of  the  charge  before  combustion. 

Q 

X  =  — -  =  ratio  of  specific  heat  of  constant  pressure  to  specific 
Cr 

heat  of  constant  volume. 

s  =  2.71828  =  io'4342945  =  the  base  of  hyperbolic,  natural, 
or  Naperian  logarithms.  Log£^4  =  2.3026  X  Iog10^4. 
Log10^4  is  the  common  logarithm  of  A. 

252.  Additional  Laws  of  a  Perfect  Gas.  —  Some  of  the  laws  of 
a  perfect  gas  have  been  given  in  Chapter  XVI.  The  last  equation 
of  section  196,  modified  as  to  subscripts,  is 

PV        T 


3/6  THE  GAS  ENGINE 

in  which  P,  F,  and  T  represent  the  pressure,  volume,  and  tem- 
perature of  a  perfect  gas  for  any  assumed  condition,  and  P0  and 
T0  may  be  taken  conveniently  as  the  pressure  and  temperature 
at  which  the  specific  volume  of  gas  is  usually  given.  F0  is  then 
the  corresponding  specific  volume.  The  latter  is  usually  given 
at  atmospheric  pressure  and  either  the  freezing  point  of  pure 
water  or  at  a  slightly  higher  temperature  that  approaches  more 
nearly  to  average  atmospheric  temperature. 

The  specific  volumes  of  actual  gases  are  given  in  Table  I  for 
both  32°  F.  and  62°  F.,  corresponding  to  491  and  521  degrees 
absolute  Fahrenheit. 

By  transposition,  the  last  equation  can  be  brought  to  the 
form 


The  expression 

— - — -  =  a  constant  for  any  particular  perfect  gas. 

Its  value  can  be  found  by  substituting  numerical  values  belonging 
to  the  gas.  The  numerical  values  must,  of  course,  accord  with 
the  system  of  units  adopted.  Thus,  for  a  pressure  of  14.7  pounds 
per  square  inch  =  2116.8  pounds  per  square  foot,  and  32°  F.  = 
491  degrees  absolute  Fahrenheit,  the  specific  volume  of  air  is 
12.39  cubic  feet  per  pound.  Therefore,  for  air,  taking  the 
pressure  in  pounds  per  square  foot  to  correspond  to  the  cubic 
foot  unit  of  volume, 


PF  =-J-8Xl2'39r  =  53.42  r, 

491 

whence 

PF 

—  =  53.42  for  air. 

The  expression  P0F0  represents,  for  any  perfect  gas,  the 
mechanical  work  done  by  its  expansion,  while,  the  pressure 
remains  constant  at  P0,  from  an  initial  condition  of  zero  volume 


THEORETICAL  HEAT  CYCLES  377 

to  a  final  condition  represented  by  P0,F0,ro.     Xhe  change  of 

y 
volume  for  each  degree  of  temperature  =  —  -•    The  mechanical 

TQ 

work  done  by  the  expansion  of  the  gas  during  a  rise  of  temperature 
of  one  degree  while  the  pressure  remains  constant  is  therefore 


When  the  temperature  is  taken  at  32°  F.  (TQ  =  491°  abs.  F.), 
the  change  of  volume  of  a  perfect  gas  for  each  degree  Fahrenheit 
change  of  temperature,  when  the  pressure  remains  constant 
during  the  change,  is  T|T  of  its  volume  at  32°  F. 

The  mechanical  work  done  by  the  expansion  of  1  pound  of 
air  while  enough  heat  is  being  added  to  it  to  increase  its  tempera- 
ture 1°  F.,  the  pressure  remaining  constant,  is,  in  accordance  with 
the  numerical  computation  just  made,  53.42  foot-pounds  for  air 
considered  as  a  perfect  gas. 

When  a  gas  is  cooled  by  abstracting  heat  from  it,  the  work  it 
does  during  contraction  is  negative.  The  amount  of  this  negative 
work  per  degree  change  of  temperature  is  the  same  as  when  the 
temperature  is  increased  one  degree,  the  pressure  remaining 
constant  in  each  case.  For  air  the  negative  mechanical  work  due 
to  cooling  1°  F.  at  constant  pressure  is  53.42  foot-pounds  as 
before. 

P  V 

—  —  °  will,  for  convenience,  be  represented  by  R.     One  of  the 

TQ 

general  expressions  of  the  relation  between  the  pressure,  volume, 
and  temperature  of  a  perfect  gas  thus  becomes 

PV=  RT. 

The  numerical  value  of  R  can  be  computed  for  any  perfect  gas 
in  a  manner  similar  to  that  by  which  it  has  been  computed  for 
air,  for  which  R  =  53.42  foot-pounds.  (This  must  not  be  taken 
to  mean  that  air  is  a  perfect  gas.) 

Another  property  of  a  perfect  gas  is  that  when  the  temperature 
of  any  given  quantity  (mass,  weight)  of  the  gas  is  increased  any 
given  amount  (as  a  specified  number  of  degrees)  by  the  addition 


3/8  THE  GAS  ENGINE 

of  heat,  the  amount  of  heat  that  is  retained  in  the  gas  to  produce 
the  given  change  of  temperature  is  always  the  same  whether  the 
pressure  or  the  volume  remains  constant  or  both  change.  The 
significance  of  this  is  that  none  of  the  heat  energy  added  is  con- 
verted into  latent  heat  for  changing  the  internal  or  molecular 
condition  of  the  gas  with  change  of  pressure,  volume,  and  tem- 
perature.* 

The  heat  which  causes  change  of  temperature  only  is  called 
"  sensible  "  heat. 

253.  Relation  between  Specific  Heat  of  Constant  Volume  and 
of  Constant  Pressure  for  a  Perfect  Gas.  —  The  specific  heat  of 
constant  volume  of  a  gas  has  already  been  defined  as  the  amount 
of  heat  required  to  increase  the  temperature  of  a  given  weight 
of  gas  1  degree  while  the  volume  remains  constant;  and  the 
specific  heat  of  constant  pressure  has  also  been  defined  as  the 
amount  of  heat  required  to  increase  the  temperature  of  a  given 
weight  of  the  gas  1  degree  while  the  pressure  remains  unchanged. 

In  the  case  of  the  specific  heat  of  constant  volume  no  external 
(mechanical)  work  is  done,  since  there  is  no  change  of  volume 
during  the  change  of  temperature. 

The  specific  heat  of  constant  pressure  includes  both  the  heat  to 

*  The  conversion  of  water  into  steam  by  the  addition  of  heat  is  an  example 
that  affords  a  means  of  conceiving  what  is  meant  by  "latent  heat."  When 
heat  is  added  to  water  after  it  has  been  brought  up  to  the  boiling  point  (about 
2i2°F.  at  atmospheric  pressure)  the  water  is  all  converted  into  steam  with- 
out rise  of  temperature  if  the  pressure  is  kept  constant.  One  pound  of  water 
at  2i2°F.  and  14.7  pounds  per  square  inch  pressure  requires  to  convert  it  into 
steam  at  the  same  pressure  and  temperature,  about  965.7  B.t.u.  of  heat. 
The  pound  of  water  makes  about  26.36  cubic  feet  of  steam  at  the  given  pressure 
and  temperature,  which  practically  measures  the  increase  of  volume  during 
the  change  from  water  to  steam.  (The  volume  of  the  water  is  so  small  in 
comparison  with  that  of  the  steam  as  to  be  negligible.) 

The  mechanical  work  done  by  the  expansion  of  the  water  into  steam  is 
therefore  (14.7  X  144)  26.36  =  55,800  foot-pounds  about,  which  corresponds 
to  55,800  •*-  778  =  71.7  B.t.u.  The  difference  between  this  last  quantity 
and  the  total  heat  of  conversion,  965.7  —  71.7  =  894  B.t.u.,  is  the  amount 
of  heat  that  has  become  latent  and  is  not  measurable  in  the  steam  as  change 
of  temperature,  or  in  mechanical  work  done  during  the  formation  of  the 
steam. 


THEORETICAL  HEAT  CYCLES  379 

increase  the  temperature  of  the  gas  1  degree  and  that  converted 
into  external  (mechanical)  work  done  by  the  expansion  of  the  gas 
at  constant  pressure  while  heat  is  added  to  increase  the  tempera- 
ture 1  degree.  It  has  been  shown  in  the  preceding  section  that 
the  external  work  done  during  1  degree  change  of  temperature 

P  V 

while  the  pressure  remains  constant  is      °^     =  R.     It  has  also 

•*  o 

been  stated  as  one  of  the  properties  of  a  perfect  gas,  that  the  amount 
of  heat  retained  in  the  gas  to  increase  the  temperature  of  a  given 
weight  of  the  gas  1  degree  is  always  the  same  whether  the  pressure 
or  the  volume  is  constant,  or  both  vary.  Therefore  the  amount 
of  heat  retained  in  the  gas  to  increase  its  temperature  1  degree 
when  the  pressure  is  kept  constant  and  the  volume  changes  is  the 
same  as  the  specific  heat  of  constant  volume  when  unit  weight 
of  the  gas  is  taken.  The  specific  heat  of  constant  pressure,  for  a 
perfect  gas,  is  therefore  equal  to  the  specific  heat  of  constant 
volume  plus  the  heat  equivalent  of  the  external  work  done  by  the 
expansion  of  the  gas  on  account  of  its  increase  of  temperature. 

The  mathematical  expressions  given  below  show  the  relation 
between  the  specific  heat  of  constant  volume  and  the  specific 
heat  of  constant  pressure  for  unit  weight  (or  mass)  of  a  perfect 
gas. 

R  GVP  PV 

=  C  +-  C+  =  C 


In  foot-pound  and  Fahrenheit-degree  units,  the  specific  heat 
of  constant  volume,  Cv,  for  air  is  .1687  B.t.u.  per  pound.  The 
value  of  R  has  been  calculated  for  air  as  53.42  foot-pounds.  The 
mechanical  equivalent  of  heat  in  the  units  taken  is./=  778  foot- 
pounds per  B.t.u.  By  substitution  in  the  above  equation, 

Cp  =  .1687  +  ^^  =  .1687  +  .0688  =  .2375  B.t.u.  for  air. 

778 

254.  Thermodynamic  Changes  in  which  One  of  the  Quantities, 
Pressure,  Volume,  Temperature,  or  Total  Heat  in  the  Gas,  Remains 
Constant.  —  The  four  methods  of  change  in  the  condition  of  a 
gas  for  which  the  relations  between  P,  F,  and  T  are  most  readily 


380 


THE   GAS  ENGINE 


computable  in  the  case  of  a  perfect  gas,  and  for  which  the  heat 
added  to  or  discarded  by  the  gas,  as  well  as  the  corresponding 
work  done,  can  also  be  mathematically  determined  for  the  perfect 
gas,  are: 

a.  Pressure    and    temperature    change    at    constant   volume. 

(Isometric  change.) 

b.  Volume  and   temperature  change  at    constant    pressure. 

(Isobaric  or  isopiestic  change.) 

c.  Pressure    and    volume    change    at    constant    temperature. 

(Isothermal  change.) 

d.  Pressure,  volume,  and  temperature  all  change,  but  no  heat 

is  supplied  to  or  abstracted  from  the  gas.     (Adiabatic 
change. ) 

In  all  the  following  changes  it  is  convenient  to  assume  that  one 
pound  of  gas  is  used. 

255.  Isometric  Change.  —  In  Fig.  121  isometric  change  is 
represented  on  the  pressure-volume  diagram 
by  the  vertical  line  1  2  parallel  to  the 
pressure  axis.  Since  the  volume  remains 
constant,  the  changes  of  pressure  and  tem- 
perature •  due  to  the  addition  or  abstraction 
of  heat  are  both  directly  proportional  to 
the  change  in  the  amount  of  heat  in  the  gas. 
The  amount  of  heat  to  be  added  to  the  gas 
to  change  its  temperature  from  Tv  corre- 
spending  to  PXF,  to  Tv  corresponding  to 


FIG.  121. 


whence 


r,   at  constant  volume  is 
H  =  Cv  (T2  -  7\), 

H  H 


The  corresponding  increase  of  pressure  due  to  the  heat  H  can 
be  determined  from  the  above  equations  by  substituting  for  Tl 
and  T  their  values  in  terms  of  the  ressure.  These  values  are 


THEORETICAL  HEAT  CYCLES 


381 


obtained  from  the  relation,  common  to  all  perfect  gases,  PV  = 
RT,  whence 

P  V  P  V 

.-Sr. 


and 


The    substitution    of   these   values    in    the    equation    H  = 
Cv  (T,  -  r,)  gives 

C  V 

H  -  -z—  (P  -  P) 
R     (F>       ^ 

P        P        — 

c,r 

The  following  equations  are  also  true  for  a  perfect  gas  at  con- 
stant volume : 

p,    r,  P2  -  pt    r,  -  rt 

—?  =  — -  •    and     —^ -  =  J •  • 

pi      Ti  pi  Ti 

There  is  no  external  (mechanical)  work  done,  since  there  is  no 
change  of  volume.     This  is  expressed  by  the  equation 

W  =  o. 

256.  Isobaric  Change.  —  In  Fig.  122  the  change  at  constant 
pressure  is  indicated  by  the  horizontal  line  1  2  parallel  to  the 


V2 


FIG.  122. 


volume  axis  of  the  diagram.  Heat  must  be  added  to  keep  the 
pressure  constant  while  the  volume  increases.  Part  of  the  heat 
added  goes  to  perform  external  work,  and  the  remainder  to  increase 
the  temperature  of  the  gas  so  as  to  maintain  a  constant  pressure. 


382  THE   GAS   ENGINE 

The  amount  of  external  (mechanical)  work  done  during  the 
expansion  of  the  gas  from  F1  to  F2  is 

W  =  P  (F2  -  V,). 

The  amount  of  sensible  heat  retained  in  the  gas  necessary  to 
increase  the  initial  temperature  7\  to  the  final  temperature  T2 
corresponding  with  the  volume  F2  is 

5  =  c,  (T,  -  r,). 

The  values  of  7\  and  T2  in  terms  of  the  corresponding  volumes 
are  determined  by  the  equation  PV=  RT,  in  which  P  is  constant 
in  this  case.  Thus, 

T,  =  -R  F2;     and     T,  --  |  Vv 

whence 

The  total  amount  of  heat  that  must  be  added  to  the  gas  to 
produce  the  change  of  temperature  and  do  the  external  work  is 

H  =  S  +  GW 

F2  -  FJ  +  GP  (F2  -  FJ 


The  relation  between  the  volume  and  the  temperature  is 

T        V  T  —  T        V   —  V 

il-J-2;    and    ii  -  -'--1-2  -  !-'. 

r,     F,'  r,  F, 

257.  Isothermal  Change.  —  In  this  case  only  enough  heat  is 
added  to  the  gas  during  its  expansion  to  keep  the  temperature 
constant. 


THEORETICAL  HEAT  CYCLES 


383 


In  Fig.  123  the  line  1  2  represents  the  general  form  of  the 
diagram  for  limited  expansion  of  a  perfect  gas  at  constant  tem- 
perature. 


•Isothermal  for 
a  Perfect  Gas. 


FIG.  123. 


The  external  (mechanical)  work  done  during  the  expansion 
from  Ft  to  F2  is  represented  by  the  area  Ftl  2F2Fr  The 
mathematical  expression  for  the  external  work  is 


W 


r 
/ 

J  v. 


PdV. 


Since  the  temperature  is  constant,  the  pressure  varies  inversely 
as  the  volume;  therefore  if  F  =  volume  at  any  point  of  the  curve, 
then 


, 
—  =  -J  l;      whence     P 


Pl      V 


PlVl 

—  -  — 
V 


By  substituting  this  value  of  P  in  the  quantity  under  the 
integral  sign,  the  equation  for  the  external  work  done  becomes 

dV 


=  P.F,  (log.F2  - 


(Loge  =  natural  log. ) 


THE   GAS  ENGINE 


For  P4Fj  may  be  substituted  the  equivalent  value  as  given  in 
the  equation  PV  =  RT  =  P1VV  whence 


Since  the  temperature  of  the  gas  does  not  change,  all  the  heat 
given  to  it  is  converted  into  mechanical  work.     Therefore 


W 
- 

J 


V 


258.  Adiabatic  Change.  —  Since  in  this  case  no  heat  is  either 
added  to  or  abstracted  from  the  gas  during  its  change  of  volume, 
the  pressure  falls  more  rapidly  during  expansion  than  for  iso- 
thermal expansion.  The  temperature  also  drops  during  expan- 


son. 


FIG.  124. 

In  Fig.  124  adiabatic  expansion  is  represented  by  the  line 
1  2.  The  initial  volume  is  Vl  and  the  final  volume  Vv 

The  external  (mechanical)  work  done  by  the  gas  during  any 
infinitesimal  increase  of  its  volume  is 


dW  =  PdV 


THEORETICAL  HEAT  CYCLES  385 

and  the  corresponding  decrease  of  sensible  heat*  in  the  gas,  as 
indicated  by  its  change  of  temperature,  is 

dS  =  CvdT. 

There  being  no  heat  added  to  or  abstracted  from  the  gas  by 
any  exterior  source,  the  change  of  sensible  heat  must  be  equal  to 
the  heat  equivalent  of  the  external  work  done.  This  is  expressed 
by  the  equation 

dS  =  -  GdW;    or    CvdT  =  -  GPdV. 

The  negative  sign  appears  in  the  last  two  equations  because 
when  positive  work  is  done  by  the  expansion  of  the  gas  it  causes 
a  decrease  in  the  sensible  heat  in  the  gas,  and  the  negative  work 
done  by  the  gas  during  its  compression  causes  an  increase  in  the 
sensible  heat  of  the  gas. 

The  last  equation  may  be  written,  for  convenience  in  further 
development,  in  the  form 

o  =  CvdT  +  GPdV. 

The  value  of  dT  can  be  expressed  in  terms  of  dV  and  dP  as 
found  from  the  equation  PV=  RT,  which,  by  differentiating, 
becomes  (remembering  that  p,  V,  and  T  are  all  variables  in 
adiabatic  change) 

PdV  +  VdP  =  RdT;     whence     dT  =  -dV  +  -dP. 

R  R 

By  substituting  this  value  of  dT  in  the  next  to  the  last  equation, 
it  becomes 

o  =  £2  VdP  +  &  +  G\  PdV 


which,  by  multiplying  by  R,  dividing  by  PV,  and  writing  for 


Cv  +  GR  its  value  Cp,  becomes 


dP      C^dV 

O  =  -  +   —  "-  -  > 

P    •  C.  V 


386  THE  GAS  ENGINE 

Q 

and  by  putting  the  ratio  — —  =  X  in  the  last  equation,  it  is  reduced 
totheform  ^ 

p  ~  l  v ' 

The  integration  of  the  last  equation  from  zero  to  the  values 
P  and  V  gives 

Constant  =  loge  P  +  I  loge  V 

=  loge  P  +  loge  V* 


whence  „,,; 

PVA  =  constant. 

Since  PF^  has  a  constant  value, 

pyX  =  p  y  X  =  p  y  X 

*   l¥  1  A   2r  2    > 

of  which  the  following  are  convenient  forms  for  application : 
p  y  X  =  p  y  X.      _2  =  [  _j  )  . 

Mri  ^2K2    >        p  \F  /     ' 

And  from  the  equation  PF=  R7^,  in  which  /?  is  a  constant  for 
any  particular  perfect  gas,  the  relations  between  the  temperatures 
and  volumes  are: 


and 


Again,  for  the  relation  between  temperatures  and  pressures, 


T        P  V        P    \P 
•*  1         *  iri         £  i     ^: 

i 

and 


Pl 


THEORETICAL  HEAT  CYCLES  387 

The  total  external  work  done  by  the  expansion  ^of  the  gas  from 
V,  to  F2  is 

W  = 

The  value  of  P  as  determined  from  the  equation  PFA  =P1F1X  is 

P  y  A  i..      i 

p  =     1    1    =  p  V    V~ 
yl 

which,  when  substituted  in  the  preceding  equation,  gives  it  the 
form 

w  -  py* 


P  F 


Or,  since  PtVt*  =  P2F2^,  the  second  from  the  last  equation 
can  be  brought  to  the  form 

P,V,     F/'1       P2F2      F/'1 


rrr    _ 

~ 


1     F-1      X  -  1 


P  7  _  P  7 

•rly  1  J  2K  2 

/t-     1 


Whence,  by  substituting  for  PiV1  its  value  RTV  and  for  P2F2  its 


value  RT2, 


T  —  T 
W  =  R± 

A    "•"" 


388  THE   GAS  ENGINE 

The  equation  for  the  change  of  sensible  heat  in  the  gas  is 
S  =  C,  (Tt  -  7\) 


c 

—» 
„ 


V  —  P  V  } 
lrl        *  lrl/J 


which  has  a  negative  value  for  expansion  of  the  gas. 

A  check  on  the  computation  can  be  made  by  use  of  the  equation 

S  -  -  GW. 

259.  Comparison  of  Expansion  and  Compression  Lines.  —  • 
Fig.  125  shows  the  relative  positions  of  the  expansion  lines  of 
a  perfect  gas  whose  initial  condition  is  A}  for  expansion  in 


Constant  Pressure 


Adiabatic  X-1.41 


FIG.  125. 

accordance  with  the  four  methods  of  expansion  for  which  equa- 
tions have  just  been  developed.  The  expansion  lines  are  respec- 
tively for  constant  volume,  constant  pressure,  for  isothermal  and 
for  adiabatic  change.  The  initial  condition  of  the  ga§  is  the  same 
in  each  case  and  is  represented  by  the  point  A.  The  constant 


THEORETICAL  HEAT  CYCLES 


389 


volume  and  constant  temperature  lines  are  the  same,  for  all  gases, 
perfect  or  imperfect.  The  isothermal  line  occupies  the  same 
position  for  all  perfect  gases.  The  adiabatic  line  is  generally 
different  for  each  gas,  or  more  definitely,  it  has  a  different  posi- 
tion for  each  value  of  the  ratio  of  the  specific  heat  of  constant 
pressure  to  the  specific  heat  of  constant  volume.  This  ratio  has 
been  distinguished  by  the  letter  A  in  the  notation.  The  adia- 
batic line  of  expansion  lies  below  the  isothermal  expansion  line. 


Isothermal 

Constant  Pressure 


FIG.  126. 


Fig.  126  shows  the  relative  positions  of  the  compression  lines 
of  a  perfect  gas,  starting  in  each  case  from  the  same  initial 
condition  A. 

260.  Theoretically  Perfect  Otto  Cycle.  -  -  Fig.  127  shows 
the  pressure-volume  diagram  of  a  theoretically  perfect  Otto 
cycle. 

As  applied  to  the  internal-combustion  motor,  the  initial  state 
of  the  combustible  charge  is  represented  by  the  point  A.  The 
charge  is  compressed  adiabatically  from  A  to  B.  It  is  then 
heated  by  its  own  total  combustion,  while  the  volume  remains 
constant  at  Vb.  During  combustion  the  pressure  rises  to  Pc 
at  C  with  a  corresponding  temperature  Tc.  The  products  of 
combustion  then  expand  adiabatically  from  Vb  back  to  the 
initial  volume  Va,  the  condition  at  the  completion  of  adiabatic 
expansion  being  represented  on  the  diagram  by  the  point  D. 
Heat  is  then  abstracted  at  constant  volume  Va  till  the  pressure 


390 


THE   GAS  ENGINE 


falls  to  the  initial  value  as  represented  by  the  point  A  and  the 
temperature  is  the  same  as  that  of  the  charge  in  its  initial  state. 
The  last  change  (the  reduction  of  pressure  and  temperature  at 
constant  volume)  has  an  approximate  equivalent  in  the  actual 
Otto  cycle  in  the  discharge  of  the  burned  gases  from  the  cylinder 
of  the  motor  and  the  taking  in  of  a  new  charge. 


FIG.  127. 


In  order  that  the  products  of  combustion,  when  brought  to  the 
initial  volume  and  pressure  of  the  charge,  Va  and  Pa,  shall  have 
a  temperature  the  same  as  the  initial  temperature  of  the  charge, 
the  conditions  are,  in  general,  that  the  specific  heats  of  constant 
pressure,  Cv  and  Cp,  of  the  burned  gases  shall  be  the  same  as  those 
of  the  combustible  charge,  and  that  the  products  of  combustion 
and  the  combustible  mixture,  when  both  are  at  the  same  tempera- 
ture and  pressure,  shall  have  equal  volumes.* 

Since  the  introduction  of  a  factor  for  the  variation  of  specific 
volume  (at  equal  temperatures  and  pressures)  due  to  combustion 
has  but  a  slight  effect  on  the  form  of  those  of  the  equations  already 
written  that  apply  to  this  cycle,  such  a  factor  /?  will  be  introduced 
for  following  out  the  cycle  mathematically.  And  since  the  in- 
troduction of  different  specific  heats  of  the  charge  and  of  the 

*  See  chapter  on  Combustion  and  Heat  Values  for  contraction  and  expan- 
sion of  specific  volume  due  to  the  chemical  reactions  of  combustion. 


THEORETICAL  HEAT  CYCLES  391 

products  of  combustion  merely  means  the  use  of  different 
values  of  the  specific  heats  and  their  ratios  in  part  of  the 
equations  that  have  been  developed,  different  values  of  specific 
heats  will  be  used.  The  following  section  treats  the  cycle  on 
this  basis. 

261.  Equations  for  Otto  Cycle.  —  In  Fig.  127  the  initial 
pressure,  volume,  and  temperature  are  Pa,  Va,  and  Ta.  The 
same  letters  with  subscripts  b,  c,  and  d  are  used  to  indicate  the 
corresponding  values  at  the  points  B,  C,  and  D  on  the  diagram. 

The  factor  /?  =  the  ratio  of  the  volume  of  the  burned  gases  to 
the  initial  volume  of  the  combustible  mixture  when  both  are  at 
the  same  temperature  and  pressure  =  the  ratio  of  the  specific 
volumes  of  the  products  and  of  the  charge. 

The  specific  heats,  Cvf  and  Cp',  and  the  ratio  of  the  latter  to 
the  former  =  A'  for  the  charge,  have,  in  general,  values  that 
differ  from  the  corresponding  values  of  C/',  Cp",  and  \"  for  the 
burned  gases.  The  combustible  mixture  and  the  mixture  of 
burned  gases  are  both  assumed  to  be  perfect  gases. 

The  equations  relate  to  a  definite  weight,  as  1  pound,  of  the 
fuel  gas. 

For  adiabatic  compression  of  the  combustible  charge  from  A 
to  B, 

PVX'  =  constant. 


The  work  done  on  the  gas  during  compresssion  is 

P  V   -  -  P  V 

W  ==     °    b         a    a 

X  -  1 
The  heat  stored  in  the  gas  during  adiabatic  compression  is 

S'-^  (PbVb  -  PJa) 
=  GW. 


392  THE   GAS  ENGINE 

Combustion  at  constant  volume  of  combustion  space 


c 
' 


P  -  SP       T-Tb 


/7~l  ft  P  T1 

tJJ-  b         •*•  b  P*b  *  b 

The  work  done  is 

W"  =  o. 

The  heat  stored  in  the  gas  during  combustion  at  constant 
volume  is 

O//     _       TT 

For  adiabatic  expansion  of  the  products  of  combustion  from 
C  to  D, 

"  =  constant. 

P  V        T 

__    rp     i   '  o  \  .        •*•  d'  a  __   •*-  d 


_  P  ALA*  - 

P*(v     ' 


The  mechanical  work  done  by  the  gas  during  adiabatic  expan- 
sion is 


The  heat  abstracted  from  the  gas  during  adiabatic  expansion  is 
S'"  =  %7  (p'v»  ~  P*VJ- 

K 
=  GW". 

Discharge  of  products  of  combustion : 

No  useful  work  is  done  during  the  discharge  of  the  products 
of  combustion  after  they  have  expanded  in  the  motor  to  the 


THEORETICAL  HEAT  CYCLES  393 

initial  volume  Va  of  the  charge.  The  portion  of  tlje  heat,  of  that 
added  to  and  stored  in  the  gas  during  compression  and  combus- 
tion, which  is  still  retained  in  the  products  of  combustion  at  the 
condition  Fa,  Pd,  Tj  is  therefore  wasted  so  far  as  transformation 
into  mechanical  energy  by  the  motor  is  concerned. 

The  heat  stored  in  the  gas  during  adiabatic  compression  and 
during  combustion  equals 

S'  +  S"  =  GW  +  Hi. 

The  heat  abstracted  during  adiabatic  expansion  equals 

S'"  =  GW'". 

The  heat  wasted  is  the  difference  between  the  quantities  repre- 
sented in  the  last  two  equations,  and  equals 

Hd  =  S'  +  S"  -  S'" 
-  GW  +  Hi  -  GW'" 
=  Hi-G  (W"  -  W). 

It  may  be  noted  that,  on  account  of  the  difference  between 
the  specific  heats  (by  weight)  of  the  charge  and  of  the  products 
of  combustion,  the  heat  that  would  be  abstracted  frorp.  the  ex- 
haust gases  by  cooling  them  to  the  initial  temperature  of  the 
charge  will  not  be  the  same  in  amount,  at  the  initial  pressure,  as 
the  wasted  heat.  The  total  heat  in  the  charge  and  in  the  dis- 
charged products  above  absolute  zero  temperature  must  therefore 
be  taken  injto  consideration  to  obtain  the  waste  heat  by  equations 
involving  temperatures.  The  practical  value  of  such  equations 
is  slight.  1  \. 

In  cases  where  there  is  no  change  of  specific  heat  the  follow- 
ing equation  can  be  applied : 

Hd  =  Cv"  (Td  -  Ta). 

Efficiency.  The  efficiency  of  the  transformation  of  heat  energy 
into  useful  mechanical  energy  during  this  theoretical  Otto  cycle 


394 


THE   GAS  ENGINE 


is  the  ratio  of  (a),  the  difference  between  the  total  heat  added  to 
the  gas  and  that  discharged  to  (b),  the  total  heat  added  by  com- 
bustion. That  is, 

Hi  -  Hd 
Efficiency  =         ^~ 

**i 

The  efficiency  can  also  be  expressed  as  the  ratio  between  the 
heat  equivalent  of  the  mechanical  work  done  and  the  total  heat 
of  combustion.  Thus, 

G  (W"f  -  W) 
Efficiency  =  ' 

262.  Efficiency  as  Affected  by  Variation  of  Compression.  - 
It  has  been  stated  that  increase  of  the  pressure  of  compression 
increases  the  efficiency  of  an  internal-combustion  motor  as  deter- 
mined in  the  actual  operation  of  the  motor.  The  reason  for  this 
can  be  shown  by  the  aid  of  the  theoretical  pressure-volume 
diagram. 


FIG.  128. 


In   Fig.    128,   suppose   that   the   theoretical   pressure- volume 
diagram  is   at  first  as  shown  by  the  full-line  diagram.     The 


THEORETICAL  HEAT  CYCLES 


395 


mechanical  work  done  is  represented  by  the  area  ,4  BCD.  Now 
suppose  that,  starting  with  the  same  amount  of  charge  at  the  same 
condition  A  as  before,  the  compression  is  carried  to  the  point  E1 
on  the  adiabatic  AB,  so  that  the  compressed  volume  of  the  charge 
is  smaller  than  on  the  full-line  diagram.  When  the  heat  added, 
as  by  combustion,  is  the  same  as  before,  the  pressure  will  rise  on 
account  of  the  added  heat  to  the  point  C',  which  is  on  an  extension 
of  the  adiabatic  line  CD.  The  expansion  will  then  follow  the 
line  C'CD.  The  new  diagram  with  the  higher  compression 
ratio  will  be  larger  than  the  first  one  by  the  area  BB'C'CB,  which 
represents  a  corresponding  increase  of  work  over  that  of  the  first 
diagram. 

The  ratio  of  the  efficiencies  of  the  two  cases  will  be  the  same 
as  that  of  the  areas  B'C'DAB'  and  BCDAB,  since  the  same 
amount  of  heat  is  added  by  combustion  in  each  case. 

263.  Effect  of  Variation  of  Specific  Volume  on  Account  of 
Combustion.  —  In  Fig.  129  the  full-line  diagram  ABCD  is  the 


theoretical  form  for  a  combustible  mixture  whose  specific  volume 
does  not  change  on  account  of  combustion.  Another  gas  which 
has  the  same  specific  heats  and  heat  value  but  whose  specific 
volume  contracts  on  account  of  the  chemical  action  of  combustion, 
will  give  the  diagram  ABC'D'AB,  in  which  the  expansion  line 
C'Df  falls  below  that  of  the  gas  that  has  no  contraction  of  specific 


396 


THE  GAS  ENGINE 


volume  on  account  of  combustion.  The  mechanical  work  that 
the  gas  whose  specific  volume  contracts  by  combustion  will  do  is 
therefore  less  per  unit  of  its  heat  value,  and  its  efficiency  will 
consequently  be  less  than  that  of  one  that  undergoes  no  con- 
traction. 

On  the  other  hand,  a  gas  whose  specific  volume  increases  by 
combustion  will  do  more  work,  other  conditions  being  equal, 
than  one  whose  specific  volume  does  not  change  by  combustion. 


(Increase  of  specific  volume  by  combustion  means  that  the  volume 
of  the  products  of  combustion  is  greater  than  that  of  the  com- 
.bustible  mixture,  both  at  the  same  temperature  and  pressure,  as 
has  been  stated  before.) 

The  effect  of  specific  expansion  of  a  gas  during  combustion  is 
indicated  by  the  dotted  line  in  Fig.  130. 

264.  Effect  of  Different  Specific  Heats  of  Combustible  Gases 
and  of  Products  of  Combustion.  —  Fig.  131.  The  full-line  dia- 
gram is  for  a  perfect  gas  whose  products  of  combustion  have  the 
same  specific  heats  as  the  combustible  charge.  Another  com- 
bustible gas  having  the  same  specific  heats  and  heat  value  but 
whose  products  have  higher  specific  heats,  will  give  the  diagram 
whose  expansion  is  represented  by  the  dotted  line.  It  will  be 


THEORETICAL    HEAT  CYCLES 


397 


seen  that  the  increased  specific  heat  has  the  effecj  of  decreasing 
the  area  of  the  diagram.  The  efficiency  is  correspondingly 
decreased. 


265.  Effect  of  Change  of  Ratio  ^  of  Specific  Heats  by  Com- 
bustion. —  If  the  ratio  of  the  specific  heat  of  constant  pressure  to 

Q 

that  of  constant  volume,  —  =  A,  is  less  for  the  products  of  com- 

Cv 

bustion  than  for  the  combustible  mixture,  then  the  expansion 
line  will  not  drop  so  rapidly  as  when  the  ratio  is  the  same  in  both 

cases. 

c 

I 


This  is  indicated  in  Fig.  132,  in  which  the  full  lines  form  the 
diagram  for  the  same  value  of  the  ratio  X  in  both  the  charge 


398 


THE   GAS  ENGINE 


and  the  products.    The  dotted  line  CD'  is  for  products  of  com- 
bustion having  a  lower  value  of  X  than  its  value  for  the  charge. 
266.   Effect  of  Imperfect  Gas  on  the  Theoretical  Otto  Cycle.  - 
The  products  of  combustion  of  the  gases  used  in  internal-com- 
bustion motors  do  not  have  constant  values  of  their  specific  heats. 
The  specific  heat  increases  with  increase  of  temperature,  and,  so 
far  as  is  known,  decreases  with  increase  of  pressure.     The  net 
result  is  generally  that  the  specific  heats  are  higher  as  the  tem- 
perature and  pressure  both  increase  on  account  of  combustion. 
While  not  positively  known,  it  will  be  assumed  for  the  purpose  of 

Q 

illustration   that   the   ratio  —  =  X  decreases  as  the  products  of 

Cv 
combustion  expand. 

The  effect  of  these  departures  from  the  properties  of  a  perfect 
gas  is  illustrated  in    Fig.    133.     The    full   line    represents  the 


theoretical  pressure-volume  diagram  for  a  perfect  gas.  The 
dotted  line  is  the  expansion  line  for  an  imperfect  gas  having  the 
properties  just  set  forth. 

On  account  of  the  increased  specific  heat  of  constant  volume, 
the  pressure  rises  only  to  Cf  instead  of  C  during  combustion.  It 
may  be  assumed  that  the  specific  heats  of  the  perfect  gas  and  of 
the  imperfect  gas  are  equal  at  B. 


THEORETICAL  HEAT  CYCLES  399 

The  decreasing  value  of  ^  as  the  gases  expand  causes  the 
line  C'D'  to  become  more  nearly  horizontal  than  a  corre- 
sponding line  for  a  constant  value  of  A,  so  that  the  terminal 
pressure  at  Dr  is  higher  than  that  for  a  perfect  gas  expanding 
from  C'. 

267.   Other  Causes  that  Modify  the  Theoretical  Otto  Cycle.  - 
The  principal  causes,  in  addition  to  those  already  cited,  that 
modify  the  theoretical   Otto   cycle   in   its  practical   application 
are  : 

1.  Heat  transfer  between  the  cylinder  walls  and  the  gas. 

2.  Combustion  is  not  at  constant  volume. 

3.  Discharge  of  products  of  combustion  is  not  at  constant 

volume  of  cylinder  space. 

4.  Leakage  of  gas  from  motor  cylinder  around   the  piston, 

valves,  etc.). 

Under  normal  conditions  of  operation  with  a  water-cooled  or 
oil-cooled  cylinder,  the  charge  of  gas  receives  heat  from  the 
metal  of  the  cylinder  at  least  during  the  early  part  of  compression. 
As  the  temperature  increases  during  compression,  it  is  possible 
that  the  gas  has  a  higher  temperature  than  the  metal  during  the 
latter  part  of  compression  and  thus  loses  heat  to  the  metal. 
During  combustion  and  at  least  the  early  part  of  expansion 
heat  is  abstracted  from  the  gas  by  the  metal.  Whether  this 
abstraction  of  heat  from  the  gas  continues  till  the  exhaust 
port  is  opened  depends  on  the  temperature  of  the  charge,  the 
extent  of  expansion,  and  the  temperature  of  the  metal.  It 
is  probable  that  the  metal  abstracts  heat  from  the  gas  during 
all  or  nearly  all  of  the  expansion  stroke  under  the  usual  condi- 
tions of  working. 

In  an  air-cooled  motor  working  with  a  very  hot  cylinder  the 
charge  probably  receives  heat  from  the  metal  during  all  of  the 
compression  stroke,  and  heat  is  abstracted  from  the  products 
during  at  least  the  early  part  of  expansion. 

The  effects  of  the  other  three  causes  are  shown  in  the  indicator 
cards  from  practice  in  the  chapter  under  that  heading. 


400 


THE   GAS  ENGINE 


268.  Modified  Theoretical  Otto  Cycle.  —  Fig.  134  shows  the 
theoretical  type  of  diagram  that  gives  the  highest  thermodynamic 
efficiency  for  cycles  of  the  nature  of  the  Otto.  The  initial  volume 
of  charge  is  Va  at  the  pressure  Pa.  It  is  compressed  adiabatically 
to  VbJ  heated  by  combustion  at  constant  volume  Vb  to  TCPC,  and 
then  expanded  adiabatically  till  the  pressure  falls  to  the  initial 
pressure  Pa  at  the  volume  Ve. 


Constant 
A         Pressure       E  ^o  A 


FIG.  134. 


Taking  Pa  =  Pe  =  atmospheric  pressure,  the  line  AE  is  a 
line  of  atmospheric  pressure.  This  corresponds  in  practice  to 
the  displacement  of  the  products  against  atmospheric  resistance 
while  the  piston  moves  from  E  to  A.  The  heat  wasted  is  that 
necessary  to  increase  the  volume  of  the  gas  from  Va  to  Ve  at 
constant  (atmospheric)  pressure.  The  area  of  the  diagram  is 
larger  than  that  in  which  the  initial  and  final  volumes  are  equal, 
by  the  amount  ADEA. 

This  diagram  is  of  the  same  nature  as  those  of  a  four-stroke 
Otto  cycle  motor  that  cuts  off  the  admission  of  combustible 
mixture  completely  when  the  piston  has  moved  only  part  way  on 
the  suction  stroke.  (See  Fig.  107.) 

While  this  cycle  has  a  high  thermodynamic  efficiency  in  relation 
to  indicated  power,  it  does  not  have  a  correspondingly  high 
efficiency  for  the  conversion  of  heat  into  delivered  mechanical 
energy  which  must  take  into  account  the  mechanical  efficiency 
of  the  machine  (motor).  At  some  point  on  the  expansion  line 
CDE  the  pressure  falls  to  an  amount  that  is  just  sufficient  to 


THEORETICAL    HEAT    CYCLES 


401 


overcome  the  mechanical  friction  of  the  motor.  4^er  this  point 
is  reached  there  is  no  gain  in  the  amount  of  power  delivered  by 
the  motor  during  the  remainder  of  the  expansion,  but  an  actual 
loss  of  power  occurs  if  expansion  is  carried  out  beyond  the  point 
just  mentioned. 


A  Constant  Y 
Pressure 


FIG.  135. 

In  Fig.  135,  if  X  is  the  point  where  the  driving  effort  of  the 
expanding  gas  and  the  frictional  resistance  of  the  machine  just 
balance  each  other,  then  this  diagram  is  the  one  for  the  maximum 
motor  efficiency  at  a  fixed  compression  pressure.  (See  Fig.  107 
for  method  of  approximating  this  diagram  in  practice.) 


Constant 


Constant  !_ 

_ — -'C 

A  Pressure 


FIG.  136. 


269.   Theoretical    Brayton    Cycle.  —  Fig.     136.     This    cycle 
theoretically  consists  in  adiabatically  compressing  a  charge  of 


402  THE   GAS  ENGINE 

non-combustible  gas  from  the  condition  A  to  B,  and  then  main- 
taining a  constant  pressure  during  the  early  part  of  the  outstroke 
of  the  piston  by  adding  more  gas  which  is  combustible  and  burns 
as  it  enters  the  motor  cylinder,  thus  increasing  the  temperature 
of  the  charge  as  the  volume  in  the  cylinder  increases.  The 
addition  and  burning  of  gas  are  stopped  at  C,  and  the  contents 
of  the  cylinder  expand  adiabatically  to  the  end  of  the  stroke. 
The  burned  gas  is  then  expelled,  while  the  volume  of  the  cylinder 
space  remains  constant,  which  completes  the  cycle. 

The  expansion  may  be  carried  to  any  point  D  on  the  adia- 
batic  DD' ',  and  the  exhaust  valve  kept  open  on  the  compres- 
sion stroke  till  the  point  A,  where  compression  is  to  begin,  is 
reached. 

270.  General   Equations   for   Thermodynamic    Change.  —  In 
the  preceding  discussion  the  equation  PV*  —  constant  has  been 
used  for  adiabatic  expansion,  in  which  X  is  the  ratio  of  the  specific 
heat  of  constant  pressure  to  that  of  constant  volume.     This 
equation  can  be  extended  to  more  general  application  by  making 
the  exponent  such  that  it  can  be  assigned  any  value.     This  is  done 
in  the  equation, 

PVn  =  constant, 

in  which  any  value  may  be  assigned  to  n. 

If  n  =  1  then  the  equation  applies  to  isothermal  expansion  or 
compression.  By  making  n  =  o  the  equation  for  constant 
pressure  is  obtained,  since  F°  =  1  and  therefore  PV°  =  constant. 
When  n  =  oo  the  equation  becomes  that  for  constant  pressure, 
since  F*  =  oo . 

For  any  finite  value  of  n,  equations  can  be  developed  for 
determining  points  on  the  expansion  and  compression  lines  of  a 
perfect  gas. 

In  view  of  the  fact  that  there  are  so  many  modifying  factors 
met  with  in  the  application  of  these  equations  to  practical  con- 
ditions, as  has  been  pointed  out  in  relation  to  the  Otto  cycle,  they 
are  of  little  or  no  use  in  practice. 

271.  Other  "Thermodynamic  Cycles.  —  It  will  doubtless  readily 
be  seen  that  by  combining  different  lines  of  expansion  and  com- 


THEORETICAL  HEAT  CYCLES  403 

pression,  an  infinite  number  of  thermodynamic  Cycles  can  be 
obtained.  In  the  present  state  of  the  internal-combustion  motor 
art  none  of  the  cycles  except  those  that  have  been  mentioned 
seem  to  find  application  however,  and  there  appear  to  be  such 
great  difficulties  in  utilizing  efficiently  cycles  other  than  the  ones 
now  in  use  as  to  prevent  their  early  application. 


CHAPTER  XXI. 
RESULTS  OF  TRIALS. 

272.  Introductory.  —  The    matter  relative    to  tests  which    is 
given  in  this  chapter  has  been  selected  on  account,  on  the  one 
hand,  of  its  covering  a  great  variety  of  bituminous  coals  and 
lignites,  and  on  the  other  hand  as  being  representative  of  modern 
gas  engine  practice  in  regular  service.     Also  because  two  kinds  of 
gas  producers  are  brought  into  consideration.     In  one  case  a  con- 
tinuous updraught  producer  was  used,  and  in  the  other  a  pair 
of  intermittent  downdraught  producers. 

273.  United  States  Government  Tests  at  St.  Louis.  —  These 
tests   were   made  largely  for  the  purpose  of  determining   the 
suitability  of  various  bituminous  coals,  lignites  and  peat  for  con- 
version into  gas  for  combustion  motor  use.     A  great  number  of 
different   coals   and  lignites   were   tested.     The   trials   were   so 
extensive,  complete  and  fully  reported  as  to  be  the  most  valuable 
information  in  this  connection.     A  very  small  proportion  of  the 
mass  of  data  will  be  presented. 

The  gas  producer  used  was  of  the  continuous,  updraught  pres- 
sure type,  of  the  general  form  of  Fig.  114.  The  gasification 
chamber  was  about  7  feet  diameter  (inside)  at  the  fire  zone.  The 
producer  was  rated  at  250  horsepower  capacity. 

The  gas  engine  was  of  the  three-cylinder,  single-acting,  ver- 
tical four-cycle  type,  rated  235  horsepower  at  200  r.p.m.  The 
engine  cylinders  were  19  inches  diameter  and  the  stroke  22 
inches. 

A  gas  J:ank  20  feet  diameter,  13  feet  high  and  of  4000  cubic 
feet  capacity  was  used  in  connection  with  the  producer. 

Steam  for  producing  the  blast  and  aiding  in  the  gasification 
of  the  fuel  was  taken  from  separate  boilers.  Power  was  used  for 
driving  the  automatic  fuel-feeding  device  attached  to  the  producer, 
and  also  for  driving  the  centrifugal  tar  extractor.  The  items  in 

404 


RESULTS  OF  TRIALS  405 

the  tables  under  headings  containing  the  words  "  equivalent  used 
by  producer  plant"  include  the  energy  of  the  steam  supplied  and 
that  used  for  driving  the  apparatus  auxiliary  to  the  producer, 
including  the  tar  extractor. 

Tables  XII  to  XVI,  compiled  from  the  report,  and  Figs.  137 
and  138,  reproduced  from  the  report,  give  several  of  the  items  of 
the  tests. 

Test  29  is  notable  on  account  of  running  continuously  for  562 
hours. 

The  fuels  used  in  tests  71-78,  lignites,  peat,  and  bone  coals, 
show  what  can  be  done  with  fuels  that  have  been  practically 
unused  in  this  country  heretofore.  Bone  coal  is  ordinarily 
thrown  out  as  waste  at  the  mines.  Some  of  that  tested  was  com- 
posed of  so  much  hard,  stony  matter  that  a  hammer  would  strike 
fire  from  it.  The  hand-picked  bone  coal  was  of  larger  sizes  than 
the  run  of  such  coal  and  therefore  was  not  as  rich  in  combustible 
matter  as  the  run  (of  bone)  on  account  of  the  softer  parts  break- 
ing off  in  small  pieces  when  the  bone  was  thrown  aside  from  the 
tipple. 

The  tar  collected  from  the  producer  gas,  as  shown  in  Table 
XIII,  represents  a  considerable  loss  of  the  heat  value  of  the  coal 
and  a  consequent  reduction  of  the  efficiency  of  the  producer,  as 
these  tests  were  carried  out.  The  tar  was  not  utilized  so  far  as 
the  production  of  power  from  the  coal  was  concerned. 

The  heat  values  of  the  tars  from  the  different  fuels  naturally 
vary  greatly  on  account  of  the  different  compositions  of  the  tars. 
Some  tars  are  black  and  heavy  as  compared  with  others.  The 
brown  tar  from  the  lignites  is  generally  much  lighter  than  the 
black  from  bituminous  coal.  The  heavy  tars  generally  have  higher 
heating  values  than  the  lighter  ones,  as  they  occur  in  connection 
with  producer  gas  manufacture. 

The  gain  in  economy  by  breaking  up  the  tar  during  the  gas- 
making  process  into  compounds  that  are  permanent  gases,  or  of 
providing  some  means  of  usefully  burning  the  tar,  will  appear 
when  the  amount  formed  in  some  cases  is  noted  as  given  in  the 
table. 


406 


THE   GAS  ENGINE 


10.05  12.05  2.05  4.05  6.05  8.05  10  05  12.05  2.05 


6.05    8.05  10.05  12.05 


FIG.  137. 

GRAPHIC  LOG  SHEET,  PRODUCER  GAS  TEST,  IOWA  NO.  2  COAL. 
From  "  Report  on  Coal-Testing  Plant, "  U.  S.  Geological  Survey,  1906. 

1.  Manometer  No.  i  at  gas  meter. 

2.  Manometer  No.  2  at  gas  meter. 

3.  B.t.u.  of  gas  by  analysis.     (Higher  value.) 

4.  B.t.u.  of  gas  by  calorimeter.     (Higher  value.) 

5.  Rev.  per  min.  of  engine. 

6.  Temperature  of  gas  leaving  producer 

7.  Amperes,  generator  load. 

8.  H.p.  of  auxiliary  motor. 

9.  H.p.  output  of  generator. 

10.  Temperature  of  gas  at  meter. 

11.  Volts,  generator  load. 

12.  Water  used  by  producer  plant 

13.  Coal  consumed  by  producer. 

14.  Cubic  feet  of  gas  produced. 


RESULTS  OF  TRIALS 


407 


PERCENTAGE  OF  CHEMICAL  COMPOSITION  OF  COAL. 


WEST  VIRGINIA  #12 
WEST  VIRGINIA  #10 
WEST  VIRGINIA  #12  BRIQ. 
PENNSYLVANIA  #2 
WtST  VIRGINIA  #8 
WEST  VIRGINIA  #6 
PENNSYLVANIA  #1 
ARKANSAS  #2 

ARKANSAS  #4  BRIQ. 
WEST  VIRGINIA  #9 
WEST  VIRGINIA  #8 
WEST  VIRGINIA  #11 
PENNSYLVANIA  #-4 
ARKANSAS  #1  BRIQ. 

WEST  VIRGINIA  #1 
ARKANSAS  #3 

KENTUCKY  #1 

WEST  VIRGINIA  #1 
ARKANSAS  #5 

ARKANSAS  #4  BRIQ. 
WEST  VIRGINIA      #4 
ARKANSA8#2  BRIQ. 
WEST  VIRGINIA      #5 
ARKANSAS  #1 

MISSOURI  #4 

WEST  VIRGINIA      #3 
INDIANA  #1  BRIQ. 
KANSAS#2  WASHED 
WEST  VIRGINIA      #2 
PENNSYLVANIA'S  BRIQ. 
INDIAN  TERRITORY  #2 

KANSAS  #1 

INDIANA  #1  WASHED 
ALABAMA  #1  BRIQ. 
ARKANSAS  #3  BRIQ. 
KENTUCKY  #2 

ALABAMA  #1 

KANSAS  #3 

ILLINOIS  #3 

MISSOURI  rl  WASHED 
KANSAS  #5 

COLORADO  #1 

INDIAN  TERRITORY#3 
INDIAN  TERRITORY  #1 
NEW  MEXICO  #  1 

KENTUCKY  #3 

KANSAS  #3 

KENTUCKY  #4 

MISSOURI  #3  WASHED 
ILLINOIS  #4 

KENTUCKY#2  BRIQ. 
ILLINOIS  #4 

ALABAMA  0-2 

WYOMING  #1 

ILLINOIS #2  WASHED 
KANSAS  #1 

IOWA  #4  BRIQ. 
MISSOURI '1  BRIQ. 
INDIANA  $-2 

INDIAN  TERRITORY  #4 
NEW  MEXICO#2  BRIQ. 


MISSOURI 

KANSAS 

IOWA 

KANSAS 

ILLINOIS 

NEW  MEXICO 

IOWA 

ILLINOIS 

TEXAS 

MISSOURI 

IOWA 

IOWA 

MISSOURI 

IOWA 

NORTH  DAKOTA 

WYOMING 

MISSOURI 


#1 

#4 

I? 

#2 
#4 

i; 

#a 

$: 

#2 
#1 
#1 
#2 
#3 


FIG.  138. 

From  "Report  on  Coal -Testing  Plant," 
U.  S.  Geological  Survey,  1906. 


408 


THE  GAS  ENGINE 


TABLE  XII. 

Average  Compositions  of  Producer  Gases  from  Various 
Bituminous  Coals  and  Lignites.* 

(See  also  Tables  XIII,  XIV,  XV,  XVI,  and  Fig.  138.) 
All  gas  made  in  the  same  producer  of  the  continuous  up-draught  pressure  type. 


Num- 
ber. 

Name  of  Coal  or  Lignite. 

Average  Composition  of  Gas  by  Volume. 
Per  cent. 

CO2 

02 

CO 

H2 

CH4 

N2 

I 

Alabama  No.  2       )  
Clean  and  hard.  ) 

8.16 

0.  10 

16.65 

7.20 

5-64 

62.  24 

2 

Colorado  No.  i  ) 

10.  II 

•55 

17-38 

11.05 

5.00 

55-9<> 

Black  lignite.  ) 

t  3 

Illinois  No.  3  

IO.  C,3 

•  i5; 

i1?.  31 

8.« 

4.46 

61  .  19 

1    O 

t  4 

Illinois  No  4 

oo 

972 

o 
.  12 

o  o 

I  C     12 

OD 

o  08 

6.  oo 

rn    06 

1  *f 

ts 

Indiana  No.  i 

•  /— 

9.89 

•25 

Ao  •  *•* 
14.  10 

y  •  y" 
9-56 

6.08 

oV  •  V'' 
60-13 

f  6 

Indiana  No.  2 

11.80 

.07 

1  1    46 

10.  60 

6.  10 

en    07 

F 

7 

Indian  Territory  No.  i  

8-25 

/ 

.  ii 

J.    L    ,   £f.W 
19-39 

7.69 

4-92 

ov  •  y  / 
59.65 

8 

Indian  Territory  No.  4  

7.29 

.236 

17.636 

10.427 

6.30 

58.109 

9 

Iowa  No   2 

10.057 

.171 

12.571 

9-529 

7.671 

60.000 

10 

Kansas  No.  5                        ) 
Fine  slack,  good  prod'r  coal  ) 

10.267 

•133 

I2.4O 

9-05 

7-417 

60  -733 

tn 

Kentucky  No.  3 
Good,  hard  producer  coal  ) 

10.87 

.29 

12-45 

10.92 

6.52 

58.95 

+  12 

Missouri  No.  2  

12.07 

.  20 

IO    ^  3 

7  6? 

6  33 

63    23 

1       ±  •* 

fll 

Montana  No.  i  

/ 

9.04 

•  36 

w<  oo 
18  67 

/  •  "o 

9OO 
.  w 

•  oj 

4   8d 

W«J  •  *J 
CQ    jo 

1    A  .3 

ti4 

North  Dakota  No.  2  ) 
Brown  lignite.            ) 

V      V4T 

8.69 

o 

•23 

•"•       •  **f 

20.90 

H-33 

*T  •  ^T- 

4.85 

0V  *  Aw 

51  .02 

ti5 

Texas  No.  i         ) 

TI.IO 

.  22 

14-43 

10.54 

7-85 

56.22 

Brown  lignite.  ) 

16 

Texas  No.  2          ) 

9.60 

.  20 

18.22 

9-63 

4.81 

57-53 

Brown  lignite.    ) 

!? 

West  Virginia  No.  i  

IO.50 

.  10 

14-34 

2.81 

5-56 

66.69 

18 

West  Virginia  No.  4  

10.  16 

•  24 

1  5.82 

1  1  .  16 

3    74 

58.88 

19 

West  Virginia  No.  7 

9.617 

.084 

*3  ' 

12-75 

10.308 

•j  •  /T- 
6.758 

60.483 

20 

West  Virginia  No.  8  

10.327 

.218 

11.927 

9-454 

6.40 

61  .672 

21 

West  Virginia  No.  9  

10.40 

.  20 

ii  .  70 

9-55 

6.60 

59-55 

22 

West  Virginia  No.  9  

8.90 

•33 

14-77 

9.508 

6.65 

59-856 

t*3 

West  Virginia  No.  12  

IO.  34 

.  12 

14.  21 

12.08 

4.61 

^7    71; 

1       O 

24 

Wyoming  No.  2  

W         O  T^ 

10.  21 

•59 

15.46 

10.79 

S-S2 

o  /    /  j 

57-43 

*  From  "  Report  on  Coal-Testing  Plant,"  United  States  Geological  Survey, 
1906.     See  pages  407  and  409  for  composition  of  coal, 
f  Gas  producer  hopper  leaked  during  these  tests. 


RESULTS  OF  TRIALS 
TABLE    XIII. 

Proximate  Analyses  of  Bituminous  Coals  and  Lignites. 
Temperatures  and  Tar  Products  of  Gasification.* 

(See  also  Tables  XII,  XIV,  XVI,  and  Fig  138.) 


409 


Number. 

Average  Composition  of  Coal. 
Per  cent. 

Total 
Coal  Con- 
sumed in 
Producer. 
Pounds. 

Total  Tar 
Collected. 

Aver- 
age 
Temp, 
of  Gas 
Leav- 
ing 
Pro- 
ducer. 
Deg. 
Fahr.f 

Mois- 
ture. 

Vola- 
tile 
Matter. 

Fixed 
Car- 
bon. 

Ash. 

Sul- 
phur. 

i  

3-76 
20.24 
7.62 
12-43 

II.  5! 

8.72 

5.00 

9.00 

16.69 
4.35 

7.28 

1  1.  60 
11.40 

39-56 

33-5° 
33-7i 
1.61 
1.99 
2.99 
2.66 
2.66 

2.22 
1-43 

9-44 

33-45 
32.26 
30.87 

32-65 
36.04 
39.60 
36.51 
33-96 
31.42 

31-97 
38.57 
35-28 

34-55 

27.78 

32.34 
29.25 
36-85 
28.89 

21  .  19 

32.58 
32.00 

3I-°5 
18.93 

35-02 

53-29 
41.65 

51-78 
45-70 
42.37 
41-95 
49-98 
40.68 

31  •  19 
52.43 
45.16 
38.28 

43-31 
26.30 
23.80 
29.76 
55-40 
60.30 
69.15 
59-oo 
59.61 
59-83 
73-19 
34.82 

9-50 
5-85 
9-73 
9.22 
10.  08 
9-73 
8-5! 
16.36 

2O-.  70 
11.25 

8-99 
14.84 
10.74 
6.36 
10.36 
7.28 
6.  14 
8.82 
6.67 
5-76 

5-73 
6.90 

6-45 
20.72 

0.86 
O.6o 
1.69 
1.41 
2.61 

4.23 

i-43 
4.12 

5-50 
3-oo 
3-86 
4-56 
1.72 

°-93 
0.63 

o-53 
0.87 

o-79 
0.92 
0.94 

I.OO 

0.79 
0.95 
3-91 

13350 
I0933 
10500 
10500 
11700 
6900 
1  1  200 
6300 

4833 
4000 

IIIOO 

33°o 

IO2OO 
13800 
12800 
9050 
6900 
2100 
6OOO 
6900 
1300 
600O 
8lOO 
I2IOO 

? 
? 
60  gal. 

75  gal- 
70  gal. 

p 

2.5bbl. 

50  gal. 
50  gal. 
? 
100  gal. 

? 
? 

5°  gal- 
150  gal. 
60  gal. 

p 
p 
? 

75  gal. 
120  gal. 
50  gal. 
50  gal. 
60  gal. 

p 
650 

753 
882 

975 
914 
? 
686 

893 
840 

p 

883 

738 
p 

•> 

559 
768 
804 
1228 
847 
752 
1064 
898 
680 

2  

7  .  . 

e 

6   . 

7  
8  

9  
10  

n  

12  

13-  • 

14 

I<r 

16   . 

17  •  • 

18  

19  

20  
21  
22  '. 
23  .  . 

24. 

*  Compiled   from  "  Report  on  Coal 
Survey,  1906. 

f  Temperature  of  gas  taken  in  main 


-Testing  Plant,"  United  States  Geological 
gas  flue  near  producer. 


4io 


THE   GAS  ENGINE 


TABLE 

Rate  of  Gasification  and  Average  Heat  Values  of  Producer 

(See  also  Tables  XII,  XIII,  XV,  XVI, 

All  gas  made  in  the  same  producer  of  the  continuous,  updraught 

at  62°  F.  and  14.7  pounds 


Number. 

Coal  per  Hour.      Pounds. 

Consumed  in  Producer. 

Equivalent  Used  by  Producer  Plant. 

Coal  as 
Fired. 

Dry  Coal. 

Combus- 
tible. 

Coal  as 
Fired. 

Dry  Coal. 

Combustible  . 

a 

b 

c 

d 

e 

/ 

g 

i 

310-5 

299.0 

280.0 

341-4 

328.7 

306.8 

2 

364-4 

290.7 

269.3 

428.4 

341-7 

316.6 

t3 

35°  -° 

323-3 

289.3 

386.0 

356.7 

319.2 

t4 

350-1 

306.3 

274.1 

398.2 

348-5 

3II-9 

ts 

394-5 

349-3 

309-5 

434-6 

384.8 

341-0 

t6 

300.0 

274.0 

244.8 

338-o 

312.0 

278.8 

7 

361  .0 

344-0 

312.0 

392-7 

374-0 

339-3 

8 

278.0 

253-2 

207.8 

312-5 

284.6 

233-6 

9 

362-5 

302.5  . 

227.5 

408.4 

340.7 

256.  2 

10 

307.8 

294-3 

259.8 

338.4 

323-6 

285.7 

tn 

370.0 

343-3 

310.0 

410.8 

381-2 

344-2 

tl2 

346.5 

306.0 

255-0 

384.5 

339-6 

283.0 

ti3 

456.5 

404  •  5 

355-8 

506.8 

449.1 

395-o 

tu 

460.0 

278.0 

249.0 

510.0 

308.0 

275-8 

fis 

590.0 

393-o 

332-o 

660.0 

439-5 

371-3 

16 

468.0 

310-3 

276.2 

5I9-5 

344-4 

306.6 

i? 

287.5 

283.0 

265-5 

320.6 

3I5-6 

296.1 

18 

233-o 

229.0 

208.0 

262.8 

258.2 

234-5 

19 

269.9 

256.9 

239.1 

299.2 

290.2 

270.  i 

20 

328.6 

320.8 

301  .  i 

364-7 

355-i 

334-1 

21 

300.0 

290.0 

274.9 

328.9 

320.1 

301.4 

22 

250.0 

244-5 

227.0 

284.8 

278-5 

258.6 

t23 

270.0 

266.1 

248.7 

3°4-9 

300-5 

280.9 

24 

403.2 

365-3 

281.6 

459-8 

416.5 

321.1 

*  Partly  from  "  Report  on  Coal  -Testing 
f  Gas  producer  hopper  leaked  during 
J  Lower  heat  values  computed  by  the 


RESULTS  OF  TRIALS 


XIV. 

Gases  from  Various  Bituminous  Coals  and  Lignites.* 

and  Fig.  138.) 

pressure  type,  about  7  feet  inside  diameter  at  fire  zone, 
per  square  inch  pressure. 


Gas  taken 


British  Thermal  Units,  Higher  Heat  Values. 

B.t.u.  per 
Cu.  Ft.  of 
Gas  Computec 
from  Average 
Chemical  An- 
alyses.   Lower 
Value.  J 

Number. 

Coal  as 
Fired  per 
Pound  . 

Dry  Coal 
per  Pound. 

Combus- 
tible per 
Pound. 

Gas  from 
one  Pounc 
Dry  Coal 
Consumed 
in  Prod'r. 

Per  Cu. 
Ft.  of 
Gas. 

k 

i 

7 

k 

I 

m 

n 

12865 

13365 

14820 

9000 

149.2 

I25 

i 

9767 

12245 

13210 

7860 

149.0 

i33 

2 

12046 

13041 

14506 

8330 

'    154.8 

"3 

3 

11237 

12834 

14344 

8840 

I5I-5 

J31 

4 

"534 

13037 

14720 

7730 

J53-7 

127 

5 

11822 

12953 

14500 

10140 

159-3 

122 

6 

12787 

!3455 

14800 

8620 

159.2 

I29 

7 

10364 

11392 

13890 

9980 

161.  i 

143 

8 

8735 

10489 

1395° 

9300 

160.  2 

136 

9 

12836 

13421 

15200 

10500 

167.2 

132 

10 

12283 

13226 

14650 

8610 

155-9 

130 

n 

10505 

11882 

14280 

8820 

140.0 

113 

12 

i°575 

H934 

13580 

6580 

160.8 

127 

13 

6802 

n255 

12600 

7830 

188.5 

J52 

14 

7267 

10928 

12945 

7260 

169.7 

144 

15 

7348 

11086 

12450 

8060 

156.2 

130 

16 

14166 

14396 

15350 

9260 

144.4 

104 

i7 

13918 

14202 

15600 

11610 

143-2 

117 

18 

14283 

14720 

15800 

13140 

154.2 

132 

19 

14168 

14558 

15470 

9070 

i55-i 

133 

20 

UI95 

14580 

15500 

8150 

151.0 

131 

21 

14224 

14548 

15650 

11380 

160.5 

134 

22 

14614 

14825 

15860 

10150 

142.5 

124 

23 

9650 

10656 

13820 

6168 

151.0 

130 

24 

Plant,"  United  States  Geological  Survey,  1906. 

these  tests. 

writer,  using  heat  values  given  in  Table  VII. 


412 


THE   GAS  ENGINE 


TABLE   XV. 

Cubic  Feet  of  Gas  from  Various  Bituminous  Coals 

and  Lignites.1* 

(See  also  Tables  XII,  XIII,  XIV,  XVI,  and  Fig.  138.) 
All  gas  made  in  the  same  producer  of  the  continuous  updraught  pres- 
sure type.     Gas  at  62°  F.  and  14.7  pounds  per  square  inch  pressure. 


Cubic  Feet  of  Gas  Produced. 

Per  Pound  Consumed  in  Pro- 

Per Pound  Equivalent  Used  by 

Number. 

ducer. 

Producer  Plant. 

Coal  as 
Fired. 

Dry  Coal. 

Combus- 
tible. 

Coal  as 
Fired. 

Dry  Coal. 

Combus- 
tible. 

0 

P 

9 

r 

S 

/ 

u 

i 

58.1 

60.4 

64-5 

52.9 

55-o 

58.9 

2 

42.1 

5^8 

57-o 

35-8 

44-9 

48.5 

t3 

49.8 

53-9 

60.2 

45-i 

48.8 

54-5 

t4 

5I-I 

58-4 

65-3 

44-8 

5i-4 

57-4 

t5 

44-5 

5°-3 

56.7 

40.4 

45-6 

5i-5 

t6 

58-2 

63.6 

7i-3 

51-6 

55-9 

62.6 

7 

51-6 

54-1 

59-4 

47-4 

49.9 

54-6 

8 

56.4 

61.9 

75-5 

50.2 

55-i 

67.1 

9 

48.5 

58-1 

77-2 

43-° 

51.6 

68.5 

10 

60.  i 

62.8 

71.2 

54-6 

57-2 

64.8 

tn 

51.2 

55-i 

61.1 

46.2 

49-7 

55-° 

tl2 

55-7 

66.0 

75-7 

50.2 

56.8 

68.2 

tl3 

36-2 

40.9 

46.5 

32.6 

36.8 

41.9 

ti4 

25.2 

41-5 

46.4 

22.7 

37-5 

41.9 

ti5 

28.4 

42.7 

50.6 

25-S 

38.2 

45-3 

16 

34-2 

51-6 

57-9 

30.8 

46.4 

52-2 

i? 

63.2 

64.  i 

68.4 

56.6 

57-5 

61.3 

18 

79.6 

81.2 

89.2 

70.6 

71.9 

79.2 

iQ 

82.5 

85-1 

91.4 

73-o 

75-3 

80.9 

20 

56-9 

58.4 

62.0 

Si-3 

52.6 

55-9 

21 

52.6 

54-o 

57-4 

48.0 

49-3 

52-3 

22 

69-3 

70.9 

76.3 

60.9 

62.2 

67.0 

t23 

70.1 

71.2 

76.2 

62.1 

63.2 

67.5 

24 

37-o 

40.9 

53-o 

35-5 

35-8 

46.5 

*  From  "Report  on  Coal-Testing  Plant,"  United  States  Geological  Survey, 
1906. 

t  Gas  producer  hopper  leaked  during  these  tests. 


RESULTS  OF  TRIALS 


413 


TABLE   XVI.  f 

Pounds  of  Various  Coals  and  Lignites  per  Brake  Horsepower 
per  Hour  Delivered  by  Gas  Engine.* 

See  also  Tables  XII,  XIII,  XIV,  XV,  and  Fig.  138. 

Three-cylinder,  single-acting  gas  engine,  19  inches  diameter  by  22 
inches  stroke.  Rated  235  brake  horsepower  at  200  revolutions  per 
minute. 

All  gas  made  in  the  same  producer  of  the  continuous  up-draught 
pressure  type,  about  7  feet  inside  diameter  at  the  fire  zone. 


No. 

Pounds  of  Coal  per  Brake  Horsepower  Hour. 

Consumed  in  Producer. 

Equivalent  Value  Used  by  Pro- 
ducer Plant. 

Coal  as 
Fired. 

Dry  Coal. 

Combus- 
tible. 

Coal  as 
Fired. 

Dry  Coal. 

Combus- 
tible. 

V 

w 

X 

y 

2 

2l 

22 

I 

1.32 

1.27 

1.19 

1-45 

1.40 

1.30 

2 

i-55 

1.23 

1.14 

1.82 

J-45 

1.34 

ta 

1.49 

1.38 

1.23 

1.64 

1.52 

1.36 

t4 

1.50 

1-31 

1.17 

1.71 

1.50 

1.34 

t5 

1.68 

1.49 

1.32 

1.85 

1.64 

1-45 

t6 

1.27 

1.16 

1.03 

1-43 

1.32 

1.18 

7 

1.50 

1-43 

1.30 

1.64 

1.56 

1.41 

8 

1.18 

i.  08 

.89 

1.33 

I.  21 

I.OO 

9 

1.56 

1.30 

.98 

1.76 

1.47 

I  .  10 

10 

i-3i 

1.25 

I.  10 

1.44 

i-37 

I.  21 

t  ii 

i-57 

1.46 

1.32 

i-75 

1.62 

1.46 

t  12 

1.48 

i-3i 

1.09 

1.65 

1-45 

I.  21 

ti3 

i-9S 

1.72 

1.52 

2.16 

1.91 

1.68 

tu 

2.91 

1.76 

1.58 

3-23 

i.  95 

1.74 

txs 

2-54 

1.69 

1-43 

2.83 

1.99 

i.  60 

16 

1.98 

J-3i 

1.17 

2.  2O 

1.46 

1.30 

17 

1.22 

1.20 

I-*3 

1-36 

1-34 

1.26 

18 

.99 

.98 

.89 

I.  12 

I.  IO 

I.OO 

19 

I-  13 

I.  10 

i.  02 

1.28 

1.24 

1-15 

20 

1^40 

1.36 

1.28 

i-55 

1-51 

1.42 

21 

1.27 

1.24 

1.16 

i-39 

i-35 

1.27 

22 

1.07 

1.04 

•97 

I.  21 

1.19 

I.IO 

t  23 

MS 

I-I3 

i.  06 

1.30 

i  28 

I    20 

24 

1.70 

1-54 

1.19 

1-94 

1.76 

1.36 

*  Compiled  from  "  Report  on  Coal-Testing 
cal  Survey,  1906. 

t  Gas  producer  hopper  leaked  during  these 


Plant,"  United  States  Geologi- 
tests. 


414 


THE   GAS  ENGINE 


TABLE  XVII. 
Proximate  Analyses  of  Bituminous  Coals.* 

Percentage  composition.     See  also  Tables  XX  and  XXII. 


No. 

Name  of  Coal. 

Mois- 
ture. 

Vola- 
tile 
Matter. 

Fixed 
Carbon 

Ash. 

Sul- 
phur. 

2  C 

Alabama  No   4  Rm 

3    Os 

2Q    £  3 

S4   78 

12    64 

I    I  ^ 

26 

Alabama  No   6  Rm           

2   44 

2S    06 

64   7c 

6    QO 

CQ 

27 

Arkansas  No.  7  A  Lump  

4.  27 

1  6  04 

67   43 

12    26 

2     IS 

28 

Illinois  No.  lyC  Rm  

0.82 

2Q    64 

SO.  34 

IO    2O 

.  4O 

2Q 

Illinois  No.  29  Lump  

14.68 

3O  .  O'C 

42  .03 

1  1  .  41 

1  .  33 

•TO 

Illinois  No    22A  Lump 

1  1    20 

3S    6c 

3Q    O4 

13    17 

4  88 

31 

Illinois  No    23  Slack 

ii  .  ^y 

II     87 

36    37 

3O    87 

II    89 

4    6^ 

72 

Illinois  No    246  Lump 

1  1  44 

33    O3 

43    O2 

IO    7l 

4    O4. 

•75 

Illinois  No.  256  Lump    

1  1   64. 

3  S    41 

44    2Q 

8  66 

341 

•74 

Illinois  No.  26  Rm.  .        

13    2O 

32    O2 

38  81 

is  88 

3    S2 

•2C 

Illinois  No.  27  Rm  

II  .  3S 

33    SO 

41  .  2C 

13  86 

4-  S4 

36 

Illinois  No.  2pB  Rm  

12.  2S 

33.  76 

41.66 

12.  22 

4.42 

77 

Illinois  No.  30  Washed  

S  .  CO 

30-  3O 

4S  .  4s 

a.66 

7.  37 

^8 

Indiana  No    12  Rm 

IO    42 

36    2Q 

4O   1^ 

1  2     ?4 

3   06 

•7Q 

Indiana  No  13  Rm.              

1  1  .  S3 

34    80 

4O   44 

13    23 

31  1 

4O 

Indiana  No.  14  Rm  

36  8c 

41    O7 

14    2O 

S    14 

4.1 

Indiana  No.  16  Rm  

7.  70 

32     32 

44   07 

1  1    02 

4   OI 

42 

Indiana  No.  i8B  Lump  

12  .  II 

34    IQ 

46   87 

6  83 

1  .44 

4-2 

Kansas  No.  6  Lump  

0.8s: 

3O.  10 

46.6? 

13.2^ 

3.04 

44 

New  Mexico  No.  3A  Rm  

3.62 

31  •  S6 

4S  •  10 

10-  63 

•  72 

4S 

New  Mexico  No.  4A  Rm  

2  .42 

34.82 

40-23 

17  .  S3 

.63 

46 

New  Mexico  No    s  Rm 

I    70 

31    32 

e  I    AC 

I  ^    4O 

66 

4.7 

Ohio  No    10  Lump 

4  05 

3O    28 

47    7^ 

8    Q2 

302 

8 

Ohio  No.  1  1  Lump           .    .    .  *  . 

344 

36  oj 

t/  •  IJ 

47    S8 

12    Q4 

4    32 

40 

Ohio  No.  12  Rm.          

3.82 

37    77 

47    42 

IO   QQ 

3    30 

SO 

Pennsylvania  No.  1  1  Rm  

i  .QS 

34   O7 

S6  6q 

7.  2Q 

1.18 

Si 

Pennsylvania  No.  12  Rm  

i  .Q£ 

3O.  SS 

S8.24 

0-  2S 

2.  10 

S2 

Pennsylvania  No.  13  Rm  

i.  6s 

33.  06 

S3-  22 

12  .07 

I.  80 

C-7 

Pennsylvania  No    i  s  Lump 

2    17 

18  09 

69  oi 

IO    33 

3O7 

c?4 

Pennsylvania  No.  16  Rm 

S     "72 

21    7C 

64    04 

7   OC 

I    60 

SS 

Pennsylvania  No.  17  Rm  

44C 

A  •  13 

28  oi 

S4   87 

12    72 

1  .  72 

56 

S7 

Pennsylvania  No.  22  Rm  
Tennessee  No.  i  Rm  

3.98 
2  .  72 

28.13 

31.  81 

57-73 

^3-  2C 

10.  if 
12  .  27 

I.OO 

1.26 

58 

CQ 

Tennessee  No.  2  Rm  
Tennessee  No    3  Rm 

3-4C 

4  88 

37.58 

34   84 

54-27 

r  7    C7 

4-75 
6   71 

.83 

i   16 

60 

Tennessee  No  4  Rm 

320 

34   4O 

S4   82 

7   4O 

88 

61 

Tennessee  No    s,  Rm 

2    S4 

34    64 

S3   06 

8  86 

7  .  7Q 

62 

Tennessee  No.  6  Rm 

3    SS 

26  oo 

40  85 

2O    S7 

6  -6V 

.  76 

63 

Tennessee  No.  7  A  Rm. 

3.O3 

34-01 

40-  21 

12.85 

3.26 

64 

Tennessee  No.  8  Washed  Rm  

2  .43 

3S  -41 

S2.  2Q 

0-87 

3-o6 

6s 

Utah  No.  i  Rm  

5.83 

42  .46 

47.  os 

4.66 

•  =?7 

66 

Virginia  No   6  Rm 

4ej 

22    77 

62    64 

10  08 

I    SO 

^Vashington  No    2  Lump 

4OI 

34   6l 

47   40 

13.80 

.38 

68 

\Vest  Virginia  No   25  Lump 

3    83 

34    34 

S3.  6l 

8.22 

.62 

63 

\Vyoming  No.  4  Rm.            .... 

II  .  3O 

4O.  32 

41  .07 

7.  31 

.28 

70 

Wyoming  No.  5  Rm.        

II  .44 

36.  37 

48.40 

3.  70 

•  Oi 

*  Compiled  from  "  Report  on  U.  S.  Fuel  Testing  Plant,"  Geological  Sur- 
vey, 1908. 

Rm.  =  run  of  mine. 


RESULTS  OF  TRIALS 


415 


TABLE   XVIII. 

Pounds  of  Bituminous  Coal  per  Brake  Horsepower   Delivered 

by  Engine.* 

See  also  Tables  XVII  and  XXI.  Three-cylinder,  single-acting  gas  engine,  19  in.  diam. 
by  22  in.  stroke,  rated  235  brake  horsepower  at  200  rev.  per  min.  All  gas  made 
in  the  same  producer  of  the  continuous  up-draught  pressure  type,  about  7  feet  inside 
diameter  at  the  fire  zone. 


No. 

Consumed  in  Producer. 

Equivalent  Value  Used 
by  Producer  Plant. 

Length 
of  Test. 
Hours. 

Total 
Coal 
Fired. 
Pounds. 

Coal  as 
Fired. 

Dry 

Coal. 

Combus- 
tible. 

Coal  as 
Fired. 

Dry 
Coal. 

Combus- 
tible. 

25 

1.  06 

1.03 

.90 

1.16 

I.  12 

•97 

24 

5,850 

26 

•77 

•75 

•7° 

.84 

.82 

.76 

5° 

9,000 

27 

I.  60 

J-53 

i-34 

•74 

.66 

i-45 

5° 

12,900 

28 

1.74 

i-57 

i-39 

.90 

•7i 

1.52 

5° 

14,400 

29 

1  .  64 

i  .40 

I  .  22 

.76 

•5° 

1.30 

562 

208,350 

3° 

1.50 

!-33 

*-I3 

•59 

.41 

i.  20 

47 

16,300 

31 

i-54 

1-36 

1.18 

•63 

•43 

1.24 

5° 

18,000 

32 

1.24 

I.  10 

•97 

•32 

•17 

1.03 

5° 

14,650 

33 

1.36 

I  .  20 

I  .02 

•43 

.27 

i.  08 

5° 

16,000 

34 

1.56 

1.36 

I  .  II 

•7° 

•47 

1.20 

5° 

16,050 

35 

2.19 

1.94 

1.63 

•36 

2.IO 

1.77 

? 

16,050 

36 

r-5* 

1-33 

I.I4 

.62 

.42 

1.22 

So 

17.250 

37 

1.38 

i-3i 

I.I7 

•45 

•37 

1.23 

5° 

16,200 

38 

1.50 

i-35 

1.16 

•59 

•43 

1.23 

5° 

17,200 

39 

1.26 

1-13 

•99 

•39 

.22 

1.07 

24 

6>75° 

40 

i-45 

i-34 

i-i3 

•54 

.42 

I  .20 

5° 

16,200 

4i 

1.82 

1.68 

1.46 

•54 

.42 

1.24 

5° 

16,100 

42 

1.26 

I.  12 

1.03 

•35 

.  2O 

I.  II 

36 

10,35° 

43 

1.41 

1.27 

i.  08 

•49 

•35 

*'1S 

i3§ 

4,5°° 

44 

I.  10 

I.  06 

•85 

.18 

.14 

.91 

5° 

12,850 

45 

1.18 

*-*5 

•99 

.29 

.26 

I.  08 

5o 

13,110 

46 

1.20 

1.18 

•99 

.29 

.26 

I.  06 

45 

12,500 

47 

I.  08 

i  .04 

•94 

•!5 

.  10 

I  .00 

.5° 

12,650 

48 

1.18 

1.14 

•99 

.26 

.22 

I.  06 

5° 

13,850 

49 

1.23 

1.18 

1.05 

•32 

.27 

I-I3 

5° 

14,35° 

5° 

I  .  22 

1.19 

I.  IO 

•32 

.29 

I.  2O 

5° 

12,200 

51 

•95 

•93 

.84 

•°5 

•°3 

•93 

28 

6,100 

52 

1.02 

I.OO 

.88 

.  10 

.09 

•95 

5° 

ii>75° 

53 

1.05 

1.03 

.92 

•J7 

.14 

i.  02 

24 

5.7oo 

54 

.85 

.80 

•74 

•95 

.90 

.82 

5° 

9.95° 

55 

I.I9 

1.14 

•99 

.26 

.21 

1.05 

5° 

13,200 

56 

I  .01 

•97 

.86 

.07 

•°3 

.92 

5° 

11,700 

57 

1.24 

1.20 

1.05 

•32 

.29 

I.  12 

So 

12,300 

58 

-95 

.92 

.87 

•°5 

.02 

.96 

5° 

11,250 

59 

I  .  10 

I.O4 

•97 

.19 

•13 

1.05 

5° 

12,950 

60 

1-13 

I.  10 

.01 

•23 

.I9 

I.  10 

50 

12,150 

61 

1.18 

I-I5 

.04 

.28 

•25 

I.  14 

5° 

12,900 

62 

i-45 

i-39 

.  10 

.  ^Q 

•53 

I  .  20 

3° 

7,95° 

63 

1.27 

1.23 

.07 

•  ^^ 

•35 

1.16 

5° 

14,400 

64 

1,18 

i-i5 

•  03 

.26 

•23 

I.  10 

24 

6,55° 

65 

i-38 

1.30 

.24 

•i7 

.  ii 

1.05 

5° 

14,250 

66 

•97 

.92 

•83 

.06 

.01 

.91 

5° 

11,000 

67 

i-i5 

i.  ii 

•95 

.22 

•17 

I  .01 

35 

9.30° 

68 

i.  ii 

1.07 

.98 

•17 

I.  12 

1.03 

50 

13,000 

69 

1.76 

1-56 

i-43 

I.9I 

1.69 

i-55 

5° 

20,200 

70 

1.36 

I.  21 

1.16 

p 

? 

? 

5° 

15.600 

*  Compiled  from  "Report  on  U.  S.  Fuel  Testing  Plant,"  Geological  Survey,   1908. 


416 


THE  GAS  ENGINE 


TABLE    XIX. 

Proximate  Analyses  of  Lignites,  Peat,  Bone  Coal,  Subbituminous, 
Semianthracite,  Anthracite,  and  Coke.* 

See  also  Tables  XX  and  XXII. 
Percentage  Composition. 


No. 

Name  of  Fuel. 

Mois- 
ture. 

Vola- 
tile 
Matter. 

Fixed 
Car- 
bon. 

Ash. 

Sul- 
phur. 

71 

Lignites  : 
Arkansas  No.  10  Rm. 

7Q      A  7 

26  49 

24     7,7 

971 

72 

Montana  No.  2  .         

8  51 

31  58 

44    ^2 

1  5    2,0 

60 

Montana  No.  3  

45.69 

74 

Texas  No.  3  Lump  

2,2.  2O 

2.0.  ii 

28.82 

8.87 

.88 

Texas  No.  4  Rm.. 

77      I  C 

2C     7,2 

7  45 

4O 

76 

Peat:f 
Florida  No.  i  Compressed  

21  .OO 

ri  .  72 

22  .  1  1 

5.  1  7 

77 
78 

Bone  coal: 
West  Virginia  No.  n  B  Hand  ) 
picked  from  waste                J  
West  Virginia  No.  24  

•47 

2.QI 

8.83 

ii.  81 

46.96 

CJ  .  IQ 

43-74 
28.08 

.27 

70 

Subbituminous  : 
\Vashington  No.  lA  Pea 

34  oo 

7.7    27 

12    56 

80 

8r 

Washington  No.  iB  Rm.  Small  sizes 
Wyoming  No.  6  Rm  

16.02 

18.26 

33-27 
37.18 

36.81 
41.82 

13.90 
2  .  74 

•59 

.47 

8? 

Semianthracite  : 
Arkansas  No.  8  

2  .  74 

0-  7O 

71.95 

15.61 

2.45 

8? 

Anthracite  : 
Virginia  No    5A  Pea 

37.4 

II  28 

67    24 

18  14 

84 

Coke: 
]V£iscell  aneous 

7  86 

60 

79 

ii  51 

I    14 

*  Compiled  from  "  Report  on  U.  S.  Fuel  Testing  Plant,"  Geological 
Survey,  1008. 

t  Peat  from  a  bog  at  Orlando,  Orange  County,  Florida,  on  the  Seaboard 
Air  Line  Railway.  The  raw  peat  contains  about  92  per  cent  of  moisture. 
The  sample  tested  was  machined  and  sun  dried.  In  this  process  the  raw 
peat  is  first  passed  through  a  condenser  to  disintegrate  it  and  destroy  the 
fiber.  It  is  then  passed  through  a  molding  machine  which  molds  it  into 
bricks  8  X  4  x  2.5  inches.  The  bricks  are  taken  to  the  drying  ground  and 
left  till  they  lose  from  60  to  75  per  cent  of  their  moisture. 

Rm.  =  run  of  mine. 


RESULTS  OF  TRIALS 


417 


TABLE   XX. 
Pounds  of  Fuel  per  Brake  Horsepower  Delivered  by  Engine.* 

See  also  Tables  XIX  and  XXII.  Three -cylinder,  single-acting  gas  engine, 
19  in.  diam.  by  22  in.  stroke,  rated  at  235  horsepower  at  200  rev.  per 
min.  All  gas  made  in  the  same  producer  of  the  continuous  up-draught 
pressure  type,  about  7  ft.  inside  diam.  at  the  fire  zone. 


No. 

Consumed  in  Producer. 

Equivalent  Value  Used 
by  Producer  Plant. 

Length 
of  Test. 
Hours. 

Total 
Coal 
Fired. 
Pounds. 

Coal  as 
Fired. 

Dry 
Coal. 

Combus- 
tible. 

Coal  as 
Fired. 

Dry 
Coal. 

Combus- 
tible. 

71 

3-°3 

1.83 

i-54 

3  •  45 

2.09 

l.76 

18 

8250 

72 

1.74 

i-59 

1.32 

1.91 

i-75 

1-45 

40 

1545° 

73 

i-39 

1.27 

1.  08 

1.48 

i-35 

*-iS 

49 

1595° 

74 

2.17 

1.47 

1.28 

2-33 

1-58 

1-38 

5° 

25500 

75 

2.16 

1.42 

1.26 

2-33 

i-54 

1.36 

5° 

2455° 

76 

2-43 

1.92 

1.79 

2-57 

2.03 

i  .90 

5° 

29250 

77 

1-65 

1.64 

.92 

? 

? 

p 

5° 

18900 

78 

1.26 

1.22 

.87 

? 

? 

p 

5° 

1  1  000 

79 

2-79 

2-34 

1.99 

2-93 

2-45 

2.08 

40 

18900 

So 

2.03 

I.7I 

1-43 

2.20 

1.85 

i-54 

14 

6550 

Si 

1.86 

1.52     . 

1.47 

2.02 

1.65 

i-59 

5° 

21900 

82 

1.58 

i-54 

1.29 

1.72 

1.67 

1.40 

26 

8550 

83 

i-i3 

1.09 

.89 

1.22 

1.18 

.96 

30 

795° 

84 

.87 

.80 

.70 

p 

p 

? 

41 

8400 

*  Compiled  from  "Report  on  U.  S.    Fuel  Testing   Plant,"   Geological 
Survey,  1908. 


4i8 


THE   GAS  ENGINE 


TABLE   XXI. 

Average  Compositions  of  Producer  Gases  from 
Bituminous  Coals.* 

See  also  Tables  XVII  and  XVIII.  All  gas  made  in  the  same  producer  of 
the  continuous  up-draught  pressure  type.  Average  composition  of  gas 
by  volume.  Per  cent. 


No. 

C02 

02 

CO 

H2 

CH4 

N2 

C2H4 

% 

IO.  I 

9  6 

17.0 

IO.  C 

14-5 
I4-Q 

1.9 
I  •  7 

56.1 

<4.  2 

•4 
i 

27 

V' 

14.    8 

12.  I 

16.1 

1.6 

CC.4 

28 
29 

3° 

ii.  6 
9.2 

9-4 

8    4. 



16.8 
20.9 

2O.  2 
2O   O 

16.2 
15-6 

13-7 
12  9 

1.9 
1.9 

2.0 

i  6 

52.9 
52.0 

54-0 

CC    7 

•3 
•4 

•7 
c 

o1 
32 

8.4 
8  t 

.  i 

22.6 
22    C 

I3'? 

13  6 

2.  I 

2    2 

52.5 
C2    0 

•  J 

•5 

r 

00 

IO    C 

10    4 

ir  .  t: 

I    7 

C2    C 

4 

0^ 

35 
36 

H 

39 

12.4 
ii.  4 
9-3 
9.0 
10.9 
o  8 

15.0 

17-3 
19.6 
19.0 

18.0 

2O   4 

12.9 
14.0 
13-8 
I3.0 
IS.2 

14-  4- 

1.6 

2.0 
2.0 
2.0 
1-9 
2    2 

57-7 
54-8 

54-7 
56.0 

53-6 

C2    7 

•4 

:! 

i  .0 

•4 
c 

4i 

11.4 

16.8 

10   4 

13-3 
16.0 

i-7 

2.  I 

56.3 
C2  .  2 

•5 
.  -i 

8    2 

21    O 

12.  7 

2.  I 

re  .4 

.6 

4,5 

92 

2O    C 

14-  "? 

2  .O 

C2  .  4 

•4 

10  6 

17    O 

12.6 

2  .O 

C7.  2 

.6 

46 

8  6 

21  .4 

14.  6 

2  .  2 

C2  .  7 

.  c 

47 

94 

2O.  7 

14.  2 

2.6 

C2.6 

.  c 

48 

9O 

2O.  2 

1C.  5 

2.  7 

C2.  ? 

.  c 

49 
5° 
Si 

9-3 
10.4 
10.8 

19.9 

18.5 

16.6 

ii   c 

15.2 
16.3 

14.9 

12.6 

2-5 
2.0 
2.4 
2  .  I 

52.6 
52-6    • 

54-8 

c;7.  i 

•5 

.2 

i 

J* 
53 
54 
55 
56 

P 

CO 

10.7 

10.  I 
IO.O 
10.  I 
IO.O 

10.9 
9  8 

.  i 

17.2 
18.2 

*7-5 
17.6 
19.6 
18.8 

2O.  2 

15.8 
15.8 

13-7 
13-3 

J5-3 
18.6 
16.5 

2.2 

2-3 

2.2 
2.2 
2.  I 
2.2 

2-4 

53-8 
S3-2 
56-1 
56.4 
52.6 
49.0 
co.  7 

•3 
•  4 
•  4 
•4 
•4 
•5 
•4 

29 
60 

IO   4 

I9.O 

,  J 
16.7 

2.4 

51.0 

.5 

61 

II    1 

I7.O 

1C.  7 

1.7 

54.2 

.5 

62 

12     3 

ICO 

14.0 

I.Q 

C.6.4 

.4 

63 
64 

65 
66 

67 
63 

II.  2 

9-7 
8-5 
10.5 

7-9 

7.0 



17.4 
I9.I 
22.2 
17.4 
22.2 
23.4 

15-3 

IS-1 
15-7 
14-3 
i5-4 
17.  i 

2-3 

2.  I 
2.6 
2.0 
2.6 
2.  I 

53-3 
53-5 
50-5 
55-5 
5i-5 
49.  i 

•5 
•5 

•5 
•3 
•4 
•4 

60 

12.  2 

•2    * 
10.4 

15.1 

2-7 

53.2 

•4 

70 

10.  I 

2O-4 

18.2 

2.6 

48.3 

•4 

*  Compiled   from 
Survey,  1908. 


Report    on  U.  S.  Fuel   Testing   Plant,"    Geological 


RESULTS  OF  TRIALS 


419 


TABLE  XXII.  f 

Average  Compositions  of  Producer  Gases  from  Lignites,  Peat, 
Bone  Coal,  Subbituminous,  Semianthracite,  Anthracite,  and 
Coke.* 

See  also  Tables  XIX  and  XX.  All  gas  made  in  the  same  producer  of  the 
continuous  up-draught  pressure  type.  Average  composition  of  gas  by 
volume.  Per  cent. 


No. 

CO2 

02 

CO 

H2 

CH4 

N2 

C2H4 

71 

17      C 

14.0 

O.  2 

2  .  4 

6O.O 

72 

13.2 

.2 

14.2 

16.0 

2.9 

52-9 

.6 

73 

8.0 

27..  2 

i">  -9 

7.  3 

49-  2 

•4 

74 

10.3 

•  7 

19.8 

14-8 

2.4 

51-3 

•7 

7c 

IO    3 

2O.  O 

IS  .4 

2  .  C 

Si.  8 

76 

12    4 

21  .O 

l8.< 

2  .  2 

4:;  .  c 

•4 

77 

0.  7 

IO.  ? 

16.6 

1.6 

52.6 

78 

12.4 

I4.O 

13.8 

I  .  2 

58.6 

7Q 

II    3 

1^4 

IO.  < 

3-6 

CO.  2 

80 

12.6 

.  2 

13-9 

12.8 

2.6 

57-4 

•7 

81 

12.  I 

l8.7 

19-3 

3-° 

46.5 

•4 

82 

n-3 

.  2 

15-9 

14.7 

I.O 

56.7 

.2 

83 

IO.  2 

19.1 

20.5 

1.9 

48.2 

.  I 

84 

92 

2IO 

ii  .  i 

.  2 

C7.  C 

.  I 

*  Compiled  from  "  Report  on  U.  S.  Fuel  Testing  Plant,"  Geological  Sur- 
vey, 1908. 


420 


THE   GAS  ENGINE 


274.   Test  of  a  soo-Horsepower  Gas  Engine  Plant  at  Worcester, 

Mass.*  —  The  gas  engine  tested  was  rated  500  horsepower  at 
155  r.p.m.  It  was  of  the  tandem,  double-acting,  horizontal, 
four-cycle  type  (four  combustion  chambers)  with  cylinders  23.5 
inches  diameter  and  a  stroke  of  33  inches,  direct  connected  to  an 
electric  generator. 

The  gas  producers  were  of  the  intermittent,  down-draught  type. 
Two  were  used  as  a  pair. 


FIG.  139.     Plan  of  Gas  Engine  Power  Plant. 

The  general  arrangement  of  the  plant  is  shown  in  Fig.  139. 
The  producers  are  shown  more  in  detail  in  Fig.  116. 

The  fuel  used  was  bituminous  coal,  except  the  lower  part  of 
the  fuel  bed,  which  was  anthracite  coal  put  on  when  building  the 
fires  at  the  beginning  of  the  test.  The  analyses  of  the  fuel  are 
given  in  Table  XXVI. 

It  is  worthy  of  note  that  the  engine  ran  at  522  brake  horse- 
power (D.h.p.)  for  six  consecutive  hours  on  gas  of  109  B.t.u.  per 
cubic  foot,  lower  heat  value,  and  that  it  ran  for  a  few  moments 
at  slightly  more  than  600  brake  horsepower,  20  per  cent  overload, 
"without  evidence  of  l  stalling.'" 

In  the  gas  producers  the  duration  of  the  run  with  steam  for 
making  water  gas  (blowing  in  steam  at  the  bottom  with  the  air 
blast  shut  off)  was  from  20  to  30  seconds.  The  ratio  of  the  time  of 
duration  of  the  water  gas  run  to  that  of  the  air  blasting  is  shown 
in  Fig.  141. 

*  Trans.  Amer.  Soc.  Mech.  Engrs.,  Vol.  29,  1907. 


RESULTS  OF  TRIALS  421 

The  " holder  drop  tests"  were  made  by  completely  cutting  off 
the  producers  from  the  gas  holder,  so  that  no  gas  was  admitted 
to  the  holder.  The  drop  of  the  holder  was  measured  as  the 
engine  drew  gas  from  it,  and  the  amount  of  gas  used  computed 
from  the  drop. 

The  " digest  of  results"  is  taken  verbatim  from  the  report. 
The  tables  and  such  of  the  figures  as  are  used  are  reproduced 
practically  unchanged.  They  are  self-explanatory.  A  few  foot- 
notes have  been  added  to  transform  certain  expressions  into  the 
terms  used  in  the  text  of  this  book. 

Lower  or  effective  heat  values  are  used  throughout  the  report. 

Digest  of  Results  of  Test  of  500- Horsepower  Gas  Engine  Plant. 

1.  Full  load  test,  51  hours  duration,  continuous  run  without 
service   interruptions   of  any  kind;   average  load   11   per  cent 
above  generator  rating,  or  practically  full  engine  rating  332  kw., 
483  b.h.p. 

2.  Fractional  load  tests  by  the  holder  drop  method;  runs  made 
at  five  different  loads,  from  no  load  to  full  engine  rating. 

3.  A  load  of  600  h.p.,  sustained  for  a  short  time  without  abnor- 
mal drop  in  speed. 

4.  Average  coal  consumption  at  the  producer,  i.4lb.  per  kw.-hr., 
equivalent  to  0.97  Ib.  per  b.h.p.  hr.,  using  Clearfield  bituminous 
run-of-mine  (14,321  B.t.u.  per  Ib.). 

5.  Average  heat  consumption  at  the  engine,  10,100  B.t.u.  per 
b.h.p.  hr.  at  full  load;  10,200  B.t.u.  per  b.h.p.  hr.  at  average  test 
load,  equivalent  to  25.29  per  cent  thermal  efficiency  *  a!  full 
rating. 

6.  Mechanical  efnciency,f  full  rating,  83.8  per  cent,  average 
test  load,  83.5  per  cent. 

7.  Average  water  consumption  for  engine  only,  9.74  gal.  per 
b.h.p.  hr.  with  66°  F.  inlet  temperature  and  47.1°  F.  rise,  equiva- 
lent to  9.4  gal.  per  b.h.p.  hr.  at  full  rating. 

*  Corresponds  to  motor  efficiency  as  defined  in  Chapter  XV. 

t  Corresponds  to  impulse-output  efficiency  as  defined  in  Chapter  XV. 


422  THE  GAS  ENGINE 

8.  Average  cylinder  oil  consumption,  1.44  gal.  per  24  hour, 
equivalent  to  0.6  gal.  per  operating  day,  or  3.2  gal.  per  operating 
week. 

9.  Speed  regulation,  no  load  to  full  load,  2.5  per  cent  above 
and  below  mean. 

10.  Average  producer  efficiency,  74.4  per  cent  at  full  load; 
73.8  per  cent  at  average  test  load  —  both  based  upon  lower  or 
effective  heat  value  of  gas. 

11.  Producer    gas,    average,    114.6   effective*    B.t.u.   during 
5 1 -hour  test;  maximum  variation  11.5  per  cent  above  and  below 
mean.     Difference  between  total  and  effective  heat  values,  about 
4f  per  cent. 


TABLE   XXIII. 
Normal  Operating  Economy. 

Averages  for  Nine  Weeks.     500 -Horsepower  Gas  Engine  Power  Plant. 

Number  of  hours  per  week  run  on  load 54-4  hours. 

Output 13500.  o  kw.-hrs. 

Average  running  load 248 .  i  kw. 

Average  running  load  per  cent  rating  of  engine 72 . 2  per  cent. 

Coal  gasified  (including  stand-by  losses) 24839 .  o  pounds. 

Coal  for  new  fires 2369 .  o  pounds. 

Coal  for  new  fires  (per  cent  of  producer  coal) 9.5  per  cent. 

Total  coal  for  all  purposes 27204. o  pounds. 

Average  total  coal  per  hour  including  new  fires 500.00  pounds. 

Coal  consumed  (excluding  new  fires)  per  kw.-hr i .  83  pounds. 

Total  coal  consumed  per  kw.-hr 2 . 015  pounds. 

*  Lower  heat  value. 


RESULTS  OF  TRIALS 


423 


TABLE  XXIV. 
5 1 -Hour  Test  of  Gas  Power  Plant. 

5oo-Horsepower  Gas  Engine.     Summary  of  Results. 


Load. 
Kilowatts  . 

Water. 
Cubic  Feet. 

Oil. 
Gallons. 

Coal.* 
Pounds. 

Quantity  at  finish  

363>55°  -° 
345,710.0 
16,840.0 
+  117.3 

i6,957-3 
51  hrs. 

332-5 

94,900  .  o 
63,560.0 
31.340.0 

2.875 

23.775 

Quantity  at  start 

"Difference      .        

2.875 

23.775 

23.775 
51  hrs. 
466 

Corrected  difference 

31,340.0 
50  hrs. 
626.8 

2.875 
48  hrs. 
0.06 

Elapsed  time 

Rate  per  hour  

Water. 
Cu.  Ft. 

Water. 
Gal. 

Oil. 
Gal. 

Coal. 
Pounds. 

Rate  per  kw.-hr  (332  .  5  kw.) 
Rate  per  b.h.p.  hr  (482  .  9  b.h.p.) 
Rate  per  i.h.p.  hr  (579  .0  i.h.p.) 

1.885 
1.078 

14.  12 

9-74 
8.075 

0.00018 
0.000125 
0.000104 

1.402 
0.965 
0.805 

*  Clearfield  run-of-mine  — 14,321  B.t.u.  per  pound  as  fired.     Average  thermal 
efficiency  of  plant,  18.43  per  cent;  engine,  24.93  Per  cent;  producer,  73.81  per  cent. 
Average  gasification  rate,  13.36  pounds  per  square  foot  per  hour.   . 


424 


THE  GAS  ENGINE 


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RESULTS   OF  TRIALS 


425 


426 


THE  GAS  ENGINE 


I 


RESULTS  OF  TRIALS 


427 


TABLE  XXVI. 

Fuel  Analysis. 
5 1 -Hour  Test  of  Gas  Power  Plant.    soo-Horsepower  Gas  Engine. 


B.t.u.      per  Pound. 

Sample. 

No. 

Volatile 

Matter. 

Fixed 
Carbon. 

Mois- 
ture. 

Ash. 

Dry. 

Actual. 

i 

I9-I5 

73-5° 

0.85 

6-5 

I43I3 

14181 

2 

20.  12 

73.60 

1.09 

5-i9 

I453I 

14360 

3 

2O.4O 

73-3° 

0.70 

5.6 

14407 

14306 

Clearfield    bitu- 

4 

18.30 

75-40 

0.90 

5-4 

14484 

14347 

minous*  used 

7 

20.78 

73.20 

0.60 

5-42 

I4531 

14445 

during  test. 

10 

20.75 

71.81 

o-75 

6.69 

14345 

14236 

i5 

19.70 

74-79 

0.90 

4.61 

14594 

14457 

18 

19.30 

76.40 

I  .00 

3-30 

14641 

14486 

20 

20.43 

71.41 

1.05 

7.11 

14232 

14069 

Average  of  9  samples.  . 

I9.87 

73-7i 

0.87 

5-54 

1445° 

14321 

Anthracite  for  building 

fires  

5-20 

78.95 

3-20 

12.65 

12709 

12320 

Ash  anthracite  f 

88.25 

I-I5 

10.6 

11977 

11840 

from  under  clinker 

87  80 

I    4.0 

10.8 

1  1946 

1  1780 

including  ash  in  pro- 

ducer ash  pits 

88.70 

o.  70 

ii  .0 

11946 

1  1850 

Averages  

88.12 

1.  08 

10.8 

11956 

11823 

*  Sulphur  in  Clearfield  Samples  2,  1.05  per  cent;  10,  0,75  per  cent;  20,  0.69  per 
cent.     Average,  0.83  per  cent. 

f  See  section  of  producer  bed,  Fig.  116. 


428 


THE   GAS  ENGINE 


Thermal  Efficiency 

Gas  Power  Plant 
The  Norton  Co. 


500 


600 


400 
Load  B.H.P. 

FIG.  142. 

The  producer  efficiency  shown  in  this  chart  is  based  on  the  lower  (effective) 
heat  value  of  the  gas. 


RESULTS  OF  TRIALS 


429 


TABLE    XXVII.  t 

Distribution  of  Heat  at  Average  Load  of  483  B.H.P. 

5 1 -Hour  .Test.     5oo-Horsepower  Gas  Engine. 


Engine 

5  only. 

Entire 

Plant. 

Brake. 

Elec. 

Brake. 

Elec. 

Useful  work  
Electrical  losses  

24.9 

22.98 

I    Q2 

18.38 

16.97 
I    41 

Friction  and  pump  work  
Jacket  absorption 

4-58 

•34.    22 

4.58 
•JA     22 

3-37 
2  r    22 

3-37 

Exhaust  and  radiation  (by  bal  ) 

l6    3 

^6    T. 

•*;>  •  ** 

26  81 

o  •  z^ 
26  81 

Loss  in  producer 

26    22 

IOO.OO 

IOO.OO 

100.00 

100.00 

TABLE   XXVIII. 
Speed  Variation  Tests.     5oo-Horsepower  Gas  Engine. 


Speed,  r.p.m  
Volts  

155 

154.0 

152.0 

2C.7  .  O 

1-50.0 

149.0 
2?8.0 

148.0 

2  ?7    O 

Amperes  

327  .  c. 

66?  .  o 

net    o 

1303.  o 

1347    O 

Kw  .  .  .? 

86.1 

170.8 

246.6 

336.  I 

346.O 

B  h  p 

I2O.  6 

247  6 

356.  5 

489  1 

503  o 

Per  cent  full  rating. 
Speed  drop,  per  cent 

25-9 

o  810 

49-5 
o  0^8 

71.2 

I    ?.Q7 

97-9 
i  916 

100.5 

2    2  "?6 

Instantaneous  Load  Test. 
No  load  to  full  load,  280  volts,  1190  amperes,  345  kilowatts,  502  brake  horsepower. 

No-load  speed 155  revolutions  per  minute. 

Load  thrown  on 148  revolutions  per  minute. 

Load  thrown  off 155  revolutions  per  minute. 

Difference 7  revolutions  per  minute. 

Speed  variation 4.6  per  cent  of  total;  2.3  per  cent  ±  mean  speed. 


430 


THE   GAS  ENGINE 


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RESULTS  OF  TRIALS 


431 


TABLE  XXX. 
Fractional  Load  Efficiencies  of  5oo-Horsepower  Gas  Engine. 


HOLDER    DROP    TESTS. 


Over- 

Nominal Load  . 

i 

} 

f 

Pull. 

load. 

Load,  brake  horsepower  

125  .00 

25O.OO 

37=C  .00 

500.00 

550.0 

Gas  cons.,*  cu.  ft.  perb.h.p.  hr... 

190.00 

I27.OO 

o  /  o 

105.5 

95.00 

92.20 

Heat  cons.,*  B.t.u.  per  b.h.p.  hr. 

2O2IO.OO 

13510.00 

11240.00 

IOIOO.OO 

9800  .  oo 

Heat  cons.,*  B.t.u.  per  kw.-hr.  .  . 

30530.00 

IQ700.00 

16340.00 

14675.00 

14300.00 

Heat  cons.,*  B.t.u.  peri.h.p.  hr.  . 

IIlSo.OO 

10600.00 

9050  .  oo 

8460  .  oo 

8295.00 

t  Thermal   efficiency,   per  cent 

brake  

12     <8 

18  84. 

21.66 

2  e    21 

2C    07 

$  Thermal   efficiency,   per  cent 

j.^  .  ^u 

X<_>  »  l*Cf 

•*J  •  *  l 

•*o  •  y  / 

electric  

ii.  16 

17.32 

20.9 

23-25 

23-85 

Thermal   efficiency,   per  cent 

indicated  

22     7? 

24  .  1 

28.  14 

30  .  I 

3O   7 

/  J 

O            1 

Equivalent  Coal  Consumption  §  for  Various  Producer  Efficiencies. 
Pounds  per  Unit  Hour. 


Producer 
Efficiency. 

Coal  Consumed  per 

Coal,  pounds. 

100  per  cent 

brake  horse  powerhour 

I-4I3 

0.994 

0.785 

0  •  7°5 

0.685 

kilowatt  hour  

2.  13 

1.376 

1.  141 

i  .025 

0.999 

80  per  cent 

brake  horse  powerhour 

1.766 

i.  812 

0.980 

0.882 

0.857 

kilowatt  hour   

2.663 

i  .  720 

i  .426 

1.281 

i  .250 

70  per  cent 

brake  horse  power  hour 

2.015 

1-347 

I  .  I2O 

i.  006 

0.977 

kilowatt  hour  

3  •  °4o 

i  .964 

1.63 

1.465 

1.426 

*  Assuming  same  coal  used  on  test  —  14,321  B.t.u. 

t  Motor  efficiency  as  used  in  text  of  book. 

{  Motor  efficiency  x  electrical  efficiency. 

§  Standard  Gas  —  106.4  B.t.u.  (effective),  62  degrees  30  inches  Hg. 


432  THE   GAS  ENGINE 

HEAT   UNITS. 

1  British  thermal  unit   =  0.252  calorie  (French). 
=  |  of  a  pound -calorie. 
=  778  foot-pounds. 

1  Calorie  (French)  =  3.9683  British  thermal  units. 
=  2.2046  pound -calories. 
=  3091  foot-pounds. 

1  Pound -calorie        =  0.4536  calorie  (French). 
„  =  i. 8  British  thermal  units. 

=  1400.4  foot-pounds. 

Molecular  heat  units :  — •  To  reduce  French  calories  to  molecular  heat  units  for 
any  substance,  multiply  the  calories  by  the  molecular  weight  of  the  substance. 
Thus,  the  heat  of  one  pound  of  carbon  burned  to  CO  is  1128  calories.  The  molec- 
ular weight  of  carbon  is  12.  The  molecular  heat  value  of  a  pound  of  carbon 
burned  to  CO  is  therefore 

12  XII28=  13,536. 

POWER. 

1  Horsepower  for  1  hour  =  2545  British  thermal  units. 

=  1,980,000  foot-pounds. 
1  Horsepower  for  1  minute  =  42.416  British  thermal  units. 

=  33,000  foot-pounds. 
1  Horsepower  for  1  second   =  .70794  British  thermal  unit. 

=  550  foot-pounds. 

PRESSURES. 

760  mm.  of  mercury  =  29  .922  in.  mercury  =  14.696  Ibs.  per  sq.  in. 
1  Centimeter  of  mercury  =  .19336  Ib.  per  sq.  in. 
1  Inch  of  mercury  =  .4908  Ib.  per  sq.  in. 
30  Inches  of  mercury  =  14.724  Ibs.  per  sq.  in. 
1  Inch  head  of  water  =  .577  ounce  per  sq.  in. 
=  .0361  Ib.  per  sq.  in. 

THERMOMETER   SCALES. 

Degrees  Fahrenheit  =  1.8  X  C°  +  32. 
Degrees  Centigrade  =  f  (F°  -  32). 


INDEX. 


ABN 

ABNORMAL  pressures,  268. 
Abrasives  for  regrinding  valve,  238. 
Absolute  zero  of  pressure,  286. 

—  temperature,  286. 
Accelerator  for  variable  speed  motor, 

*55- 

Accumulators,  electric,  90. 
Adiabatic  change  of  gas,  384. 
Adjustments,  instructions  for,  190. 
Advancing  the  spark,  149. 
Air,  carbureted  for  gas,  360. 

—  composition  of,  296. 

—  heating  for  mixture,  57. 

—  moisture  in,  320. 

—  preheating  for  mixture,  58. 

—  saturation  of,  with  fuel,  56. 
Air  cooling  the  motor,  3. 

Air  gap  width  in  spark  plug,  79. 
Air-gas  making,  334. 
Air  jacket,  3. 

Air  lock  in  fuel  supply  system,  61. 
Air  pump  for  two-cycle  motor,  25. 
Air  valve,  compensating,  49. 
Air  valve  of  carbureter,  49. 
Altitude  and  pressure  decrease,  286. 
Ammeter  for  testing  electric  batteries, 

93- 

Analyses,  moisture  in  gas,  324. 
Asphyxiation  by  exhaust  gases,  177. 
Aspirator     for     drawing     gas    from 

mains,  362. 
Atkinson  motor,  15. 
Atomic  weights,  table,  297. 
Atomizer  for  heavy  oil  fuel,  38. 


BAT 

Automobile,  adjusting  carbureter  on, 
198. 

—  compound  motor,  42. 

—  control  of  motor,  147,  153. 
Automobile  motor,  air  cooled,  8. 

control  of,  147,  153. 

valve  timing,  204. 

BACKFIRING,  101,  235. 

—  adjustment  for,  193. 

—  causes  of,  214. 

—  screen  to  prevent,  23,  27. 
Back  pressure,  180. 

exhaust,  180. 

indicator  card  showing,  271. 

momentary  increase  of,  256. 

Baffle  plate  on  piston,  35. 
Batteries  compared  for  ignition,  93. 
Battery,  testing  electric,  93. 

—  accumulator,  90. 

—  charging  storage,  90. 

—  charging,  rectifier  for  alternating 
current,  92. 

—  connection  for  ignition,  88. 

—  current  of,  85. 

—  dynamo  and  storage,  for  ignition, 
106. 

—  electric,  for  starting,  72. 

—  elements  of  electric,  84. 

—  exhausted,  89. 

—  floated  on  the  line,  106. 

—  ignition,  83. 

—  incorrect  connections,  88. 

—  multiple  connected,  86. 


433 


434 


INDEX 


BAT 

Battery,  multiple  series,  87. 

—  parallel  connected,  86. 

—  recuperating,  90. 

—  series  connected,  84. 

—  storage,  90. 

—  testing  for  positive  and  negative,  91. 

—  troubles,  213. 

—  voltage  of,  84. 

Battery  coil  of  induction  coil,  81. 
Beau  de  Rochas  cycle,  5. 
Blast-furnace  gas,  358. 
Brayton  cycle,  theoretical,  401. 
Bray  ton  motor,  27. 
British  thermal  unit,  denned,  276. 
Bulb,  ignition  with  hot,  34. 

—  torch  for  heating,  35. 

CALORIFIC  power  of  fuel,  denned,  296. 
Calorimeter  determinations  and  effi- 
ciencies, 301. 

—  tests  of  gas,  continuous.  363. 

—  error  of,  364. 
Cam,  12. 

Cam  shaft,  speed  of,  2. 
Carbon,  combustion  table,  309. 

—  in  cylinder,  235. 

—  removing,  236. 
Carburation,  47. 

—  of  air,  methods,  4. 

—  surface,  etc.,  59. 

—  to  saturation  point,  56. 
Carbureter,  adjusting  on  automobile, 

198. 

—  adjustment  of,  191. 

—  auxiliary  flame  for  heating,  58. 

—  cooled  by  vaporization,  57. 

—  diaphragm  feed,  53. 

—  disk  feed,  52. 

—  double,  57. 

—  early  forms,  59. 

—  float  feed,  49. 

—  freezing  by  vaporization,  57. 

—  fuel  supply  for,  61. 


COM 
Carbureter,  general  types,  56. 

—  heating,  57. 

—  hot-water  jacket  for,  57. 

—  ice  and  frost  in,  57. 

—  ice  in,  removing,  240. 

—  in  place,  2. 

—  kerosene,  58. 

—  leaky  float,  repairing,  239. 

—  multiple  nozzle,  51. 

—  for  non-volatile  liquids,  58. 

—  primer  for,  47. 

—  pump  feed,  52. 

—  repairs,  239. 

—  spray  nozzle,  48. 

—  spray  type  in  general,  54. 

—  water  in,  218. 

—  waterlogged  float,  239. 

—  with  water  nozzle,  57. 
Carbureter  air  valve,  49. 
Carbureter  measuring  cup,  52. 
Carbureter  throttle,  49. 
Carbureter  troubles,  212. 
Carbureter  valve,  54. 
Charge,  large  after  cut-out,  263. 

—  precompression  of,  24. 

—  saturated  and  diluted,  56. 

—  stratification  of,  27,  133. 
Choke  coil  for  ignition  system,  71. 
Coal,    composition,    chart    showing, 

407. 
-  table,  409,  414,  416,  427. 

—  cubic  feet  of  gas  per  pound,  table, 
412. 

—  gas  from,  table,  410. 

—  pounds  per  horse  power,  table,  413, 

4*5>  4i7- 

—  rate  of  gasification  of,  410. 
Coal  gas,  333. 

Coke,  composition  of,  table,  416. 
Coke  oven  gas,  359. 

composition  of,  360. 

Combustible  liquids,  care  and  han- 
dling, 243. 


INDEX 


435 


COM 

Combustible  mixture,  range  of,  4. 
Combustion,      change      of     specific 

volume  due  to,  293. 
—  chemical  equations  for,  297. 

—  complete  and  incomplete,  295. 

—  constant  heat  of,  296. 

—  at  constant  pressure,  27. 

—  denned,  4,  293. 

—  drop  of  pressure  after,  316. 

—  extinguished  by  small  ducts,  319. 

—  imperfect,  for  over-rich  mixture, 

3*9- 

—  pressures  of,  316. 

—  of  producer  gas,  312. 

—  rate  affected  by  compression,  151. 

—  rate  of,  317. 

—  of  retort  gas,  313. 

—  specific  heat  changed  by,  396. 

—  specific  heat  ratio  changed,  397. 

—  temperatures  of,  20,  316. 

—  time  of,  defined,  318. 

—  unusual  pressures  of,  318. 

—  variation  of  volume  due  to,  293, 

395- 

Combustion  chamber,  defined,  r. 
Combustion  space,  pockets  in,  268, 

3i7- 
Complete  expansion  engine,  134. 

—  indicator  card,  260. 
Compound  motors,  41. 

—  with  two  crank  shafts,  43. 
Compressed  air  for  starting  the  mo- 
tor, 38. 
Compression,  adjusting,  34. 

—  curve  for  gas,  370. 

—  economy  gain  by,  5. 

—  efficiency  affected  by,  394. 

—  heat  of,  for  igniting,  37. 

—  indicator  card  for  variation  of,  274. 

—  lost  suddenly,  236. 

—  relieving,  for  starting  the  motor, 
181. 

—  varied  by  valve-chest  cover,  27. 


CRA 

Compression  cylinders  for  two-cycle 
motors,  24. 

Compression  fuel  tank,  53. 

Compression  space,  defined,  i. 

Compression  tanks  for  Brayton  mo- 
tor, 27. 

Compression  test  by  hand,  231. 

Compressor  plant,  central,  28. 

Compressors,  auxiliary,  24,  27. 

Condenser,  electric,  for  induction 
coil,  82. 

Connecting  rod,  varying  length  to 
adjust  compression,  34. 

Connections  for  gas  motor,  33. 

Constant  pressure  combustion,  27. 

Control,  accelerator  for,  155. 

—  of  motor,  115. 

—  throttle  and  spark,  153. 
Conversion  tables,  432. 
Cooler,  165. 

—  exhaust  jets  for,  16. 
Cooling  effect  of  vaporization,  57. 
Cooling  fan,  8. 

Cooling  flanges,  8. 
Cooling  system,  138. 

—  troubles,  211. 
Cooling  the  motor,  2,  3. 

—  power  affected  by  hot  and 
cool  cylinder,  162. 

—  methods,  162. 
thermal  circulation,  165. 

—  by  vaporization  of  water,  35. 
water  consumption,  421. 

—  with  air,  163. 
with  oil,  3,  168. 

—  with  water,  164. 

Cooling  water,  adjusting  flow  of,  190. 

—  heats  unduly,  causes,  220. 

—  vaporized,  35. 
Crank  for  starting,  8,  184. 
Crankshafts,  2. 

—  double,  43. 

—  rotation  of,  per  impulse,  44. 


INDEX 


CUT 

Cut-out  indicator  diagram,  259,  262. 
Cycle  of  motor,  defined,  5. 

—  Beau  de  Rochas,  5. 

—  Brayton,  27,  401. 

—  diagram  for  complete  theo- 
retical, 371. 

—  effect     of     imperfect     gas, 

398. 

—  modifying  causes,  399. 

-  Otto,  5. 

Otto  theoretical,  389. 

—  theoretical  heat,  374. 
Cylinder,    carbon    deposit    and    re- 
moval, 235. 

—  cracked,  cause  of,  241. 

—  cracked  or  porous,  230. 

—  denned,  i. 

—  headless,  20. 

—  open  at  both  ends,  20. 

—  pockets  in,  268,  317. 

—  scored,  cause  of,  241. 
Cylinder  heads,  elimination  of,  20. 
Cylinder  jacket,  3. 

Cylinders,  arrangement  of,  44. 

DEAD  center  of  motor,  202. 
Decomposition  of  gas,  315. 
Deflector  plate  on  piston,  36. 
Density  of  gases,  284. 

-  table  of,  285. 

Diagram,  nature  for  indicator,  373. 
Diagrams,  indicator,  251. 

—  pressure- volume,  367. 

Diesel  motor,  indicator  card,  267. 

Diesel  oil  motor,  37. 

Dissociation  of  gases,  315. 

Dynamo,  see  also  Magneto  and  Gen- 
erator. 

Dynamo,  automatic  cut-out  for,  no, 
in. 

—  test  of,  224,  227. 

Dynamo-battery  ignition  system,  106. 

Dynamo  troubles,  214. 


EXH 
ECONOMY,  276. 

—  based  on   calorimeter  determina- 
tions, 301. 

—  of  fuel,  277. 

—  of  motor,  denned,  278,  279. 

—  of  plant,  defined,  282. 
Efficiencies,  comparison  of,  283. 
Efficiency,  276. 

—  compression  effect  on,  394. 

—  free-piston  motor,  40. 

—  gas  turbine,  3. 

—  impulse-output  of  motor,  defined, 
279. 

—  mechanical,  of  motor,  defined,  280. 

—  of  motor,  defined,  278. 

—  of  plant,  defined,  282. 

—  power  plant,  366. 

—  producer,  equation    for    commer- 
cial, 366. 

—  producer,  from  trial,  422. 

—  tar  loss,  405. 

—  thermal,  of  motor,  defined,  281. 

—  thermodynamic,  defined,  281. 
Electric  generators,  see  also  Dynamo 

and  Generator. 

for  ignition,  69. 

Energy,  equations  for,  367. 

—  unit  of,  defined,  276. 
Engine,  see  also  Motor. 

—  "complete  expansion,"  18,  134. 
Equalizer  for  gas  pressure,  33. 
Equations,  general,    for    thermody- 
namic change,  402. 

Exhaust,  asphyxiation  by,  177. 

—  auxiliary,  16. 

—  back  pressure  of,  180. 

—  back  pressure,  indicator  card  show- 
ing, 271. 

—  detection  of  CO  in,  193. 

—  momentary  increase  of  back  pres- 
sure, 256. 

—  mufflers,  1 78. 
—  silencing,  177. 


INDEX 


437 


EXH 

Exhaust,  submerged,  179. 

—  test  for  excess  of  fuel,  193. 
Exhaust  gases,  disposal  of,  177. 
Exhaust  jets  for  air  circulation,  16. 
Exhaust  pipe  for  scavenging,  40. 
Exhaust  port,  auxiliary,  8,  15. 
Expansion,  complete,  in  motor,  19. 
Expansion,  curve  for  gas,  370. 

—  frequency  of,  44. 

Explosion  pressures,  abnormal,  268. 
Explosions,  sharp,  264. 

—  local,  in  cylinder,  253. 

FAN  for  cooling,  8. 

Flame  propagation,  rate  of,  257,  317. 

Float,  repairing  leaky,  239. 

Foot-pound,  denned,  276. 

Free-piston  motor,  39. 

Freezing  of  carbureter,  57. 

Friction    due   to    carbon    deposit   in 

cylinder,  232. 
Fuel,  carburation  with  non-volatile, 

58. 

—  calorific  power  of,  defined,  296. 

—  composition,  table,  427. 

—  control  of  power  and   speed  by 
regulating,  115. 

—  defined,  4. 

—  economy  of,  277. 

—  excess  of,  detection  in  exhaust,  193. 

—  heat  value,  defined,  296. 

—  injecting  liquid,  5. 

—  mixing  with  air,  4. 

—  per  horse  power  per  hour  in  service, 

35i- 

—  proportion   range  in   combustible 
mixture,  4. 

—  pulverized,  4. 

—  troubles,  212. 

Fuel    economy,    pounds    per    horse 
power,  table,  413,  415,  417. 
—  shown    by   commercial    plant, 


GAS 

Fuel  economy,  trial  for,  422. 
Fuel  mixture,  rich  and  lean,  191. 
Fuel  oil,  burning,  28. 

—  injected  by  compressed  air,  37. 
Fuel  pipes,  61. 

Fuel  pump,  52. 

—  for  oil,  30,  62. 

Fuel  supply  for  carbureter,  61. 
Fuel  tank,  53. 

—  location  of,  for  safety,  244. 
Fuel  valve,  10. 

Fuels,  326. 

—  for  suction  producer,  347. 

GAS,  adiabatic  change  of,  384. 

—  analysis  relative  to  moisture,  324. 

—  blast-furnace,  358. 

—  calorimeter  tests,  continuous,  363. 

—  coke-oven,  composition  of,  360. 

—  comparison  of  expansion  lines,  388. 

—  composition   of,   table,   408,   418, 
419. 

—  composition  of,  from  trial,  graph, 
426. 

—  compression  curve  of,  370. 

—  cubic  feet  per  pound  of  coal,  412. 

—  expansion  curve  of,  370. 

—  heat  values,  table,  309,  310,  410. 
trial,  422. 

—  imperfect,    effect    on    theoretical 
cycle,  398. 

—  isobaric  change  of,  381. 

—  isometric  change  of,  380. 

—  isothermal  change  of,  382. 

—  laws  of  perfect,  285,  375. 

—  measuring,  by  drop  of  holder,  421. 

—  moisture  in,  320,  324. 

—  observation  of  quality,  362. 

—  petroleum  gas,  360. 

—  physical  properties  of,  284. 

—  producer  gas,  combustion  of,  312. 
heat    value    from    analysis, 


438 


INDEX 


GAS 

Gas,  producer  gas,  temporarily  rich, 
310. 

—  removal  of  moisture  from,  324. 

—  retort  gas,  combustion  of,  313. 

—  specific  volume,  denned,  284. 

—  thermodynamic  changes,   theoret- 
ical, 379. 

—  variation  in  quality  from  producer, 
361. 

Gas  connections,  33. 

Gas  holder,  measuring  by  drop  of, 

421. 
Gas  making,  326. 

—  air  gas,  efficiency  limit,  335. 

—  air  and  carbon  dioxide  process, 
350. 

—  blowing  the  producer,  420. 

—  calorimeter    tests,    continuous, 

363- 

—  carbureted  air  gas,  360. 

—  combined  suction  and  pressure 
producer,  351. 

—  continuous   pressure   producer, 
348. 

—  cubic  feet  per  pound  of  coal, 
table,  412. 

—  distillation  of  volatile  parts,  335. 

—  economizer,  338. 

—  efficiency  basis,  365. 

—  efficiency,   equations   for   com- 
mercial, 366. 

—  efficiency  from  trial,  428. 

—  efficiency  of  producer,  trial,  422. 

—  equations    for    proportions    of 
gases,  344,  346. 

—  exhaust    from    motor    fed    to 
producer,  350. 

—  fuels  for  suction  producers,  347. 

—  gasoline  gas,  360. 

—  intermittent  processes,  355. 

—  intermittent,     twin    producers, 
356. 

—  meters  for  gas,  366. 


GAS 

Gas  making,  moisture  separator,  338. 

—  observation  of  quality  of  gas, 
362. 

oil-water  gas,  360. 

—  petroleum  gas,  360. 
-preheater,  338. 

—  preheating      air      by      motor 
exhaust,  339. 

-  producer  gas,  337. 

—  producer,  downdraught,  350. 

—  producer  plant,  352. 

—  producer,  underfeed,  350. 

—  producers  in  pairs,  355. 

—  producers,  miscellaneous  types, 

354- 

-  purifier,  338. 

—  rate  of,  table,  410. 

-  retort  gas,  333. 

—  scrubber  for  gas,  338. 

—  stoking  the  fuel,  348. 

—  tar  destruction,  361. 
tar  loss,  405. 

—  tar,  quantity  of,  349. 

—  tar,  table  of,  409. 

—  temporary  richness  of  gas,  346. 

—  theoretical  case,  340. 

—  variation  in  quality  of  gas,  361. 

-  water  gas,  336. 
Gas  meter,  366. 

Gas  producer,  suction  type,  337. 

-  twin,  357. 
-types  of,  327. 

Gas  pump  for  two-cycle  motor,  25. 
Gas  tank,  404. 
Gas  turbine,  3. 
Gasification,  rate  of,  410. 
Gaskets,  169. 

—  stoppages  by,  240. 
Gasoline,  care  and  handling,  243. 
Gasoline  gas,  360. 

—  removing  water  from,  243. 

—  straining,  243. 
Gasoline  pipes,  244. 


INDEX 


439 


GAS 

Gasoline   tank,   location   for   safety, 

244. 

Gear,  cam-shaft,  2. 
Gears,     marking,    for    replacement, 

201. 
Generator,  electric,  magneto,  101. 

—  for  ignition,  69. 

—  oscillating,  73. 
troubles,  214. 

—  with  interrupted  magnetic  cir- 
cuit, 76. 

Governing,  38,  116. 

—  accuracy  of  different  methods  com- 
pared, 157. 

—  automatic  cut-off,  125. 

—  by  exhaust  valve,  119. 

—  by  fuel  valve,  120,  130. 

—  by  inlet  valve,  125. 

—  by  throttling,  122. 

—  by  varying   amount   of  fuel   per 
charge,  122. 

—  hit-or-miss,  117,  118. 

—  large  charge  after  cut-out,  262. 
Governing  and  hand  control,  116. 
Governor,  123. 

—  for  oil  motor,  32. 

—  for  timer,  155. 

—  pendulum,  118. 

Governors,  centrifugal  and  hydrau- 
lic, 146. 

HAMMERING  in  motor,  causes,  217. 
Hand  control,  manipulation  of,  147, 

153- 

Hand  control  and  governing,  116. 
Heat,  distribution  of,  trial,  429. 

—  latent,  defined,  378. 

—  sensible,  378. 

—  specific,  constant  volume  and  con- 
stant pressure,  378. 

Heat  cycles,  theoretical,  374. 
Heat  value,  deduction  per  pound  of 
hydrogen,  308. 


1C.N 

Heat  value,  deduction  per  pound  of 
steam,  308. 

—  error  of  determining,  364. 

—  from    analysis,    producer    gas, 

3«- 

—  lower,  defined,  305. 

—  of  fuel,  defined,  296. 
Heat  values,  higher,  defined,  305. 

-  of  gas,  table,  309,  310,  410. 

—  of  hydrogen,  305. 

—  lower,  defined,  306. 

—  variable,  in  mixtures,  332. 
Heat  units,  compared,  432. 

—  molecular,  432. 
Heating  air  for  charge,  57. 
Heating   due   to    carbon   deposit   in 

cylinder,  236. 

Heating  the  carbureter,  57. 
Hit-or-miss  governing,  115. 
Hornsby-Akroyd  motor,  28. 
—  indicator  card,  266. 
Horse  power,  defined,  276. 

conversion  table,  432. 

indicated,  249. 

Hose,  loose  lining  in,  112. 

Hot-tube  ignition,  112. 

Hot-wire  ignition,  114. 

Humidity,  determination  of,  325. 

Hydrocarbons,  314. 

Hydrogen,  heat  deduction  per  pound, 

308. 

—  heat  values,  305,  306. 

ICE,  removing  from  carbureter,  240. 
Igniter,  double  make-and-break,  66. 

—  hammer  blow  type,  69. 

—  insulation  for,  67. 

—  low-tension,  with   solenoid   circuit 
breaker,  72. 

—  make-and-break,  64. 

—  rotary,  68. 
Ignition,  63. 

—  accidental,  sources  of,  244. 


440 


INDEX 


IGN 

Ignition,  adjusting,  194. 

—  adjusting  the  timer,  207. 

—  advancing  and  retarding,  149. 

—  advancing,  for  increased  speed,  275. 

—  alternating,  current  rectifier,  92. 

—  at  atmospheric  pressure,  39. 

—  batteries  for  electrical,  71,  83. 

—  battery  floated  on  the  line,  106. 

—  break-and-make,  64. 

—  by  compression  in  oil  motor,  31. 
Diesel  motor,  37. 

—  by  hot  vaporizer,  31. 

—  by  overheated  motor,  113. 

—  catalysis  method,  114. 

—  comparing  time  in  different  cylin- 
ders, 208. 

—  comparison    of   high-tension    sys- 
tems, 99. 

—  contact  points,  material  for,  66. 

—  double,  63. 

—  dynamo-battery    system,     storage 
battery,  106. 

—  dynamo  cut-out,  automatic,   no, 
in. 

—  early  and  late,  148. 

—  electric  supply  for,  69. 

—  generators  for  electric,  66. 

—  heating  motor  by  late,  150. 

—  high-tension  distributer  system,  98. 

—  high-tension  electric  in  general,  77. 

—  high-tension  magneto,  77. 

—  hot-bulb,  34. 

—  hot-metal,  113. 

—  hot -tube,  112. 

—  hot-wire,  114. 

—  indicator  card  showing  premature, 

273- 

—  indicator  cards  showing  effect  of 
time  variation,  271. 

—  induction  coil,  77,  81. 

—  in  small  chamber,  253,  264. 

—  jump-spark,  77. 

—  lag  of,  75,  149,  152. 


IND 

Ignition,  late,  indicator  diagram,  265. 

—  low-tension,  64. 

—  magneto,  10. 

—  magneto  for  jump-spark,  102. 

—  make-and-break,  64. 

—  one  induction  coil  for  two  cylinders, 
100. 

—  pilot  flame  for,  27. 

—  platinum-sponge,  114. 

—  premature,  192. 

—  reversal  of  motor  by  early,  150. 

—  strength  of  spark  variation,  274. 

—  testing  the  batteries,  93. 

—  time  of,  13. 

—  time  affected  by  compression,  34, 

151- 

—  timer  for,  77,  80. 

—  timing- valve  for  hot-tube,  112. 

—  wiring  scheme,  95,  97. 
Ignition  system,  choke  coil  for,  71. 
desirable   features  of    low -ten- 
sion, 73. 

—  in  place,  2. 

—  kick-coil  for,  71. 

—  testing,  221. 

—  with  magneto,  jump-spark,  102. 
Ignition  troubles,  212. 
Illuminants,  314. 

Impulse,  frequency  of,  44. 
Impulse-output  efficiency  defined,  279. 
Indicated  horse  power,  249. 
Indicator,  stop  and  weak  spring  for, 
248. 

—  vibration  of,  253. 

Indicator    card,   complete  expansion 
engine,  260. 

—  Diesel  motor,  267. 

—  effect  of  speed  variation,  274. 

—  effective  or  net  area  of,  247. 

—  for  dilute  mixture,  273. 

—  for  two-cycle  motor,  251. 

Hornsby-Akroyd  motor,  266. 

impulse  loop,  248. 


INDEX 


441 


IND 

Indicator     card,     Koerting     motor, 
267. 

—  late  ignition,  265. 

—  nature  of,  373. 

—  negative  area  of,  247. 

—  negative  loop,  248. 

—  positive  area  of,  247. 

—  positive  loop,  248. 

—  premature  ignition,  273. 
-pumping,  249.     p 

—  showing  cut-out,  259,  262. 

—  showing  variation  of  compres- 
sion, 274. 

—  weak  spring,  246. 
Indicator  cards  from  practice,  245. 

—  representing  American  practice, 
251. 

—  showing  effect  of  change  of  time 
of  ignition,  271. 

—  valve  setting  incorrect,  268. 
Indicator  connections,  245. 
Induction  coils,  81. 
Induction  coil,  condenser,  82. 

—  for  ignition,  77. 

—  trouble,  213. 

—  voltage  for  operating,  83. 

—  without  interrupter,  106. 
Inflammation,  318. 
Injecting  liquid  fuel,  5. 
Injector  nozzle  for  oil  fuel,  31. 
Interrupter  of  induction  coil,  81. 
Isobaric  change  of  gas,  381. 
Isometric  change  of  gas,  380. 
Isothermal  change  of  gas,  382. 

JACKET  of  cylinder,  3. 
Jump-spark  ignition,  77. 

KEROSENE  carbureters,  58. 
Kerosene  motor,  16. 
Kick  coil  for  ignition,  71. 
Kicking  of  motor,  235. 
Koerting  two-cycle  motor,  24. 
indicator  card,  267. 


MIX 

LATENT  heat,  denned,  378. 
Launch  motor,  adjusting,  198. 
Leakage   shown   on   indicator   card, 

259,  262. 
Leaks  in  motor,  tests  for,  230. 

—  between  cylinder  and  water 
jacket,  detection  of,  232. 

—  hydrostatic  test  for,  233. 
Lignites,  gas  from,  table,  410. 

—  composition  of,  table,  409. 
Lubrication,  171. 

—  adjustment  of,  190. 

—  oil  consumption  by  trial,  422. 
Lubricators,  174. 

MAGNETO,    see    also    Dynamo    and 

Generator. 
Magneto  electric  generator,   10,   70, 

101. 

—  high  tension,  77,  102. 

—  remagnetization  of,  225. 

—  test  of,  224. 
Mean  effective  pressure,  249. 

—  equation  for,  372. 
Measuring  cup  of  carbureter,  52. 
Mechanical  efficiency  of  motor,  de- 
fined, 280. 

Metering  gas,  366. 

Mietz  &  Weiss  oil  motor,  35. 

Misfiring,  causes  of,  216,  220. 

—  test  for,  223. 

Mixture,  combustible,  4. 

—  dilute,  indicator  card  showing, 

273- 
— . —  effect  of  moisture  in,  321. 

heating  air  for,  57. 

over-rich,  detection  by  exhaust, 

193- 

over-rich,  imperfect  combustion 

of,  319. 

—  perfect,  defined,  318. 

perfect,  rate  of  burning,  318. 

proportioning  device,  124. 


442 


INDEX 


MIX 

Mixture  combustible,  rich  and  lean, 
191. 

—  saturated  air,  4. 

—  saturated  and  diluted,  56. 

—  variable  in  heat  value,  332. 
Moisture  in  air  and  gas,  320. 

—  determination  of,  325. 

—  gas  analysis  relative  to,  324. 

—  in    mixture,    effect    on    power   of 
motor,  321. 

—  precipitation  by  cooling,  321. 

—  precipitation  by  sudden  expansion, 

324- 

—  reduced  by  compression,  324. 

—  removal  from  gas,  324. 

—  table,  322. 

—  —  producer  gas,  324. 
Moisture  separator,  338. 
Motor,  see  also  Engine. 

—  air  cooled,  8. 

—  air  pump  for  two-cycle,  25. 

—  Atkinson,  15. 

—  automobile,  8. 

—  Brayton,  27, 

—  capacity  dependent  on  heat  value 
of  mixture,  332. 

—  cleaning,  235. 

—  complete  diagrammatic,  2. 

—  compound,  41. 

—  compression  pumps  for  two-cycle, 

~«3* 

—  cooling,  2. 

—  cylinder  open  at  both  ends,  20. 
— Diesel  oil-burning,  37. 

—  disabled,  running  of,  239. 

—  efficiency,     mechanical,     denned, 
280. 

—  efficiency  at  part  load,  from  trial, 

43i- 

—  efficiency  by  trial,  421,  428. 

—  erratic  behavior  of,  219. 

—  error  of  heat  value  unfavorable  to, 
365- 


MOT 

Motor,  four-cycle,  7. 
—  four-cycle  Otto,  10. 

—  four-cycle,  not  reversible,  46. 

—  free-piston,  39. 

—  fuel  economy  in  service,  351. 

—  fuel  economy,  table,  413,  415,  417. 

—  gas  pump  for  two-cycle,  25. 

—  Gobron-Brillie,  20. 

—  heat  consumption  of,  421. 
—  Hornsby-Akroyd,  28. 

—  kerosene,  16. 

—  kicking  of,  235. 

-  Koerting  two-cycle,  24. 

—  leaks,  running  test  for,  231. 

—  liquid  fuel,  28. 

—  mechanical  efficiency  of,  denned, 
280. 

—  non -compressing,  5. 

—  Nuremberg,  20. 

—  oil-burning,  28. 

—  oil-cooled,  3,  16,  168. 

—  operation,  method,- 5,  13. 

—  operation  of  two-cycle,  22. 

-  pioneer,  39. 

—  ports  of,  10. 

—  power   affected  by  heat  value  of 
mixture,  332. 

—  priming,  50. 

—  pumping  loop  for  two-cycle,  indi- 
cator card,  251. 

—  speed  variation  of  governed,  trial, 
429. 

—  starling,  181. 

—  tandem,  14. 

—  tests  for  leaks,  230. 

—  three-port  valveless,  22. 

—  traction  engine,  16. 

—  two-cycle,  7,  21. 

—  two-cycle,  power  capacity,  22. 

—  two-cycle  reversible,  46. 
-types,  i. 

—  valveless,  22. 

—  vaporizer  for  oil  fuel,  28. 


INDEX 


443 


MOT 

Motor  economy,  defined,  277. 
Motor  efficiency,  defined,  278. 
Motor  guaranty  based  on  calorimeter 

determined  values,  304. 
Motor  trials,  results  of,  16,  404,  430. 

—  5oo-horsepower  motor,  420. 

—  graphic  log  of,  406,  425. 

—  summary  of,  423,  424. 
Motor  troubles,  210.  • 
Muffler  cut-out,  180. 
Muffler  for  exhaust,  178. 

NOZZLE  for  gasoline  spray,  57. 
—  for  injecting  fuel  oil,  31. 
Nuremberg  motor,  20. 

OIL-BURNING  motors,  28. 

-  fuel  for,  28. 

Oil  consumption,  lubricating  oil,  trial, 

422. 

Oil-cooled  motor,  3,  16,  168. 
Oil  fuel,  atomizer  for  heavy,  38. 

—  injected  by  compressed  air,  37. 

—  injecting  system  for  motor,  32. 
Oil  gas  from  petroleum,  360. 

Oil  motor,  adjusting,  199. 

-  Diesel,  37. 

Oil  pump  for  fuel,  30. 

—  for  lubricating  oil,  gear  type, 

139- 
Otto  cycle,  5. 

—  effect  of  imperfect  gas  on,  398. 

—  modified  theoretical,  400. 

—  modifying  causes,  399. 

—  theoretical  equations,  389,  391. 
Overheating    and     loss     of    power, 

causes,  220. 
—  ignition  by,  113. 

PACKING,  materials  for,  169. 
Peat,  composition  of,  table,  416. 
Perfect  gas,  laws  of,  285,  375. 
Petroleum,  gas  from,  360. 


POW 

§ 


Pioneer  motors,  39. 
Pipe  stoppages,  240. 
Piston,  area  of,  249. 
—  baffle  plate  on,  35. 

—  cracked,  gasoline  test  for,  242. 

—  deflector  plate  on,  36. 

—  leaky,  cause  of,  241. 

—  oil-cooled,  3. 

—  trunk  type,  i,  3. 

—  water-cooled,  3,  167. 
Piston  rings,  3. 

—  gummed,  236. 

joints,  3. 

leaky,  230. 

—  loose,  242. 

—  peening  to  expand,  241. 

• removing  and  replacing,  242. 

Pitting  of  valve,  237. 
Plant  economy   and   efficiency,    de- 
fined, 282. 

Platinum -sponge  ignition,  114. 
Pocket    in    combustion    space,    268, 

3i7- 
Ports,  i,  10,  19. 

—  at  middle  of  cylinder,  21. 

—  auxiliary  exhaust,  15. 
Pounding  of  motor,  causes,  217. 
Power  affected  by  heat  value  of  mix- 
ture, 332. 

—  by  preheating  the  charge,  60. 
by  time  of  ignition,  149. 

—  conversion  table,  432. 

—  equations  for,  250. 

—  hand  control  of,  147. 

—  unit  of,  defined,  276. 
Power  decrease,  cause  of,  218. 
Power  less  than  it  should  be,  causes 

of,  219. 

—  lost  suddenly,  236. 

Power    plant,    distribution    of   heat, 

trial,  429. 
economy    of    operation,    trial, 

422. 


444 


INDEX 


POW 
Power  plant,  efficiency,  366. 

—  plan  of,  420. 

—  trial  by  holder  drop  test,  430. 

—  trial,  data  from,  428. 

—  trial,  graphic  chart,  425. 

—  trial  of,  404. 

—  at  Worcester,  Mass.,  trial  of,  420. 
Precompression,  27. 

—  for  two-cycle  motor,  24. 

—  of  air  for  charge,  27. 
Preheating  air  for  mixture,  58. 

—  the  charge,  effect  on  power,  60. 
Preignition,  235. 

—  causes  of,  217. 

—  indicator  card  showing,  273. 
Pressure,  abnormal,  of  explosion,  268, 

318. 

—  relief  valve  for,  145. 

—  absolute  zero  of,  286. 

—  barometer  and  manometer,  432. 

—  of  combustion,  316. 

—  of  combustion,  unusual,  268,  318. 

—  decrease  with  altitude,  286. 

—  mean  effective,  equation  for,  372. 

—  water  and  mercury,  432. 
Pressure  equalizer  for  gas,  33. 
Pressure-volume  diagrams,  367. 
Primary  coil  of  induction  coil,  81. 
Primer  for  carbureter,  47. 
Priming  the  motor,  50. 
Priming  valve,  6,  185. 
Producer  gas,  combustion  of,  312. 

—  composition,    table,    408,    418, 
419. 

—  composition  from  trial,  graph, 
426. 

—  heat  value  of,  422. 

—  heat  value  from  analysis,  311. 

—  heat  value,  table,  410. 

—  observation  of  quality,  362. 

—  temporarily  rich,  319. 
variation  in  quality,  361. 


ROT 

Producer  plant,  352. 
Producer  test,  graphic  log  of,  406. 
Producer  trials,  404. 
Producers,    combined    pressure   and 
suction  type,  351. 

—  continuous  downdraught,  350. 

—  continuous  pressure  type,  248. 

—  continuous  updraught,  328,  330. 

—  efficiency  basis  of,  365. 

—  efficiency  from  trial,  422,  428. 

—  error  of  heat  value  favorable  to,  365. 

—  fuels  for  suction  type,  347. 

—  grate  efficiency,  equation  for,  366. 

—  miscellaneous  types,  354. 

—  suction  type,  337. 

—  twin,  355. 

—  twin  intermittent,  357. 

—  types  of,  327. 

—  underfeed  type,  350. 

Pump  for  circulating   cooling  water 
or  oil,  16,  166. 

—  for  fuel,  52,  62. 

—  for  lubricating  oil,  139. 

—  packing  for,  1 70. 

Pumping  card   (indicator  diagram), 

267. 
Pumping  loop  of  indicator  card,  248. 

for  two-cycle  motor,  251. 

Purifier  for  gas,  338. 

RADIATOR,  16,  166. 

Rectifier  for  alternating,  electric  cur- 
rent, 92. 

Regrinding  a  valve,  238. 

Relief  valve  for  compression,  6. 

Retarding  the  spark,  149. 

Retort  gas,  combustion  of,  313. 
—  making,  333. 

Reversing  rotation   of  motor  crank- 
shaft, 46. 

Rings  for  piston,  3.  ^ 

Rotation  of  crankshaft  per  impulse,  44. 


INDEX 


445 


SAT 

SATURATED  mixture,  56. 

Saturation  and  dilution   of   charge, 

,    56. 

Scavenging  the  motor,  40,  129. 

Screen,  wire,   to  prevent   backfiring, 

23,  27. 

Scrubber  for  gas,  338. 
Secondary  coil  of  induction  coil,  82. 
Shaft,  cam,  2. 

—  crank,  2. 

Smoke  in  exhaust,  from  fuel,  193. 
—  from  lubricating  oil,  190. 
Spark,  variation  of  strength,  274. 
Spark  plug,  78. 

—  air  gap,  width  of,  79. 

—  cleaning,  237. 

—  testing,  222. 

—  troubles,  '212. 

Spark-plug    coil   of   induction    coil, 

82. 
Specific  heat  of  gases,  defined,  289. 

—  relation  between  constant 
volume  and  constant  pressure,  378. 

table  of,  290. 

—  variation  of,  316. 

—  variation  effects  by  com- 
bustion, 396. 

volumetric,  291. 

Specific  heats,   change   of  ratio   by 

combustion,  397. 
Specific   volume    of   gases,    defined, 

284. 

—  changed  by  combustion, 

293,  39°- 

—  factor    of    variation    for, 

39°- 

—  table,  285. 
Speed,  hand  control  of,  147. 

—  regulation  of,  117. 

Speed  variation,  effect  on  indicator 
card,  274. 
—  by  trial,  429. 


TJES 

Spray  nozzle,  57. 
Springs,  valve,  4,  119. 
Starting  the  motor,  181. 

— •  battery  for  ignition  when,  72. 

—  blank  cartridge  for,  188. 

—  by  compressed  air,  38,  145, 
189. 

—  by  hand,  184. 

—  by  its  own  impulse,  186. 

—  by  mechanical  power,  185. 

—  crank  for,  8. 

—  on  compression,  186. 

—  - preparations  for,  182. 

—  relieving    compression    for, 
181. 

—  stresses  due  to,  188. 

—  warming  for,  185. 
Steam,  heat  of,  302. 

—  heat  deduction  per  pound,  308. 
Storage  battery,  90. 
Stratification  of  charge,  27,  133. 
Supply  tank  for  fuel,  53. 

TANKS,  compressed  air,  37. 

—  constant-level  water  tank,  36. 

—  for  fuel,  61. 
-  for  gas,  404. 

Tar,  amount  produced,  409. 

—  burning  apparatus,  350. 

—  composition  of,  315. 

—  destruction  of,  in  gas  making,  361. 

—  loss  due  to,  405. 

—  quantity  in  gas  making,  349. 
Test  for  air  and  gas  leaks,  230. 

—  hydrostatic,  233. 
— with  compressed  air, 
232. 
Temperature,  absolute  zero  of,  286. 

—  of  combustion,  20,  316. 
Terminals  of  induction  coil,  82. 
Testing  the  ignition  system,  221. 
magneto  generator,  224. 


446 


INDEX 


THE 

Thermal  circulation  of  cooling  water, 

165. 
Thermal  efficiency  of  motor,  defined, 

281. 
Thermodynamic  change,  adiabatic, 

384- 

—  comparison  of  lines,  388. 

—  constant  pressure^  381. 

—  equations,  general,  401. 

—  isobaric,  381. 

—  isometric,  380. 

—  isothermal,  382. 

—  of  perfect  gas,  379. 
Thermodynamic   efficiency,    defined, 

281. 
Thermometer  scales,  conversion  of, 

432- 

Throttle,  49. 

Thumping  of  motor,  causes,  217. 
Timer  for  high-tension  ignition,  80. 

—  adjusting,  207. 

—  adjusting,  for  reversing  rotation  of 
motor,  46. 

—  advancing,   for    increased    speed, 

275- 

—  function  of,  77. 

—  governor  for,  155. 

—  speed  of  rotation  of,  81,  100. 

—  troubles,  213. 
Timing  the  valves,  200. 
Torch  for  heating  hot  bulb,  35. 
Traction  engine  motor,  16. 
Trembler  of  induction  coil,  81. 
Trial  of  motor,  16. 

—  data  from,  428. 

Trial  of  power  plant,  425. 

—  at  Worcester,  Mass.,  420. 
—  by    U.     S.    government, 
404. 
Troubles,     remedies     and     repairs, 

210. 

Trunk  piston,  3. 
Turbine  gas  motor,  3. 


VAL 

Two-cycle  motor,  21. 

—  compression  cylinders  for,  24 

—  Koerting,  24. 

—  operation  of,  22. 

—  power  capacity  of,  22. 

UNITS  of   energy,  power  and   heat, 
defined,  276. 

conversion  tables, 

432. 

VALVE,  4. 

—  automatic  inlet,  13. 

—  auxiliary  exhaust,  8,  16. 

—  disabled,  running  motor  with,  239. 

—  fuel,  ii. 

—  inlet,  hollow,  8. 

—  method  of  opening,  13. 

-  pitting  of,  237. 

—  regrinding,  238. 

—  relief,  for  high  explosion  pressure, 

6,  145- 

—  for    starting    motor    with     com- 
pressed air,  187. 

—  for  timing  ignition,  112. 

-  warping  of,  237. 

—  water-cooled  exhaust,  127,  167. 
Valves,  i. 

—  arrangement  of,  31. 

—  concentric,  8,  140. 

—  testing,  for  leaks,  232. 

—  timing  of,  200. 

Valve  mechanism,  130,  136. 
Valve  setting,  see  also  Valve  timing, 
200,  204. 

indicator  card  showing,  268. 

Valve  spring,  4. 

repairing,  239. 

strength  of,  119. 

Valve  stem,  binding  or  sticking,  236. 
Valve  timing,  see  also  Valve  setting. 

automobile  motor,  204. 

dead  centers  for,  202. 


INDEX 


447 


VAL  WOR 

Valve  timing,  effect  of  worn  and  loose  Volume  of  gases  changed  by  com- 
parts, 206.  bustion,  293,  395. 
—  marking     the     flywheel      for,  —specific,  285. 


205. 
Vaporization,      cooling      effect 

57- 

Vaporizer,  ignition  by  hot,  31. 
—  for  oil  motor,  28. 
Vibrator  of  induction  coil,  81. 


Voltmeter  for  testing  electric  batter- 
of,          ies,  93. 

WATER  tank,  constant  level,  36. 
Weights  of  gases,  284. 
Work,  equations  for,  367. 


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12 


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Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  00 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  00 

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13 


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14  . 


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15 


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*  Fischer's  Physiology  of  Alimentation Large  12mo,  2  00 

de  Fursac's  Manual  of  Psychiatry.      (Rosanoff  and  Collins.)..  .  .Large  12mo,  2  50 

Hammarsten's  Text-book  on  Physiological  Chemistry.     (Mandel.) 8vo,  4  00 

Jackson's  Directions  for  Laboratory  Work  in  Physiological  Chemistry .  .8vo,  1  25 

Lassar-Cohn's  Practical  Urinary  Analysis.      (Lorenz.) 12mo,  1  00 

Mandel's  Hand-book  for  the  Bio-Chemical  Laboratory 12mo,  1  50 

*  Pauli's  Physical  Chemistry  in  the  Service  of  Medicine.      (Fischer.)  ..12mo,  1  25 

*  Pozzi-Escot's  Toxins  and  Venoms  and  their  Antibodies.     (Cohn.).  .  12mo,  1  00 

Rostoski's  Serum  Diagnosis.      (Bolduan.) 12mo,  1  00 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  00 

Whys  in  Pharmacy 12mo,  1  00 

Salkowski's  Physiological  and  Pathological  Chemistry.      (Orndorff.)  ....8vo,  250 

*  Satterlee's  Outlines  of  Human  Embryology 12mo,  1  25 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students 8vo,  2  50 

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in  the  Practice  of  Moulding 12mo,  3  00 

Iron  Founder 12mo,  2  50 

Supplement 12mo,  2  50 

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*  Iles's  Lead-smelting 12mo,  2  50 

Johnson's    Rapid    Methods   for    the   Chemical   Analysis   of   Special   Steels, 

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Keep's  Cast  Iron 8vo,  2  50 

Le  Chatelier's  High- temperature  Measurements.     (Boudouard — Burgess.) 

12mo,  3  00 

Metcalf's  Steel.      A  Manual  for  Steel-users 12mo,  2  00 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.      (Waldo.).  .  12mo,  2  50 

Ruer's  Elements  of  Metallography.      (Mathewson) 8vo, 

Smith's  Materials  of  Machines 12mo,  1  00 

Tate  and  Stone's  Foundry  Practice 12mo,  2  00 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  00 

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Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.  A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  00 

West's  American  Foundry  Practice 12mo,  2  50 

Moulders'  Text  Book 12mo,  2  50 

16 


MINERALOGY. 

Baskerville's  Chemical  Elements.      (In  Preparation.). 

Boyd's  Map  of  Southwest  Virginia .  Pocket-book  form.  $2  00 

*  Browning's  Introduction  to  the  Rarer  Elements 8vo,  1  50 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.) 8vo,  4  00 

Butler's  Pocket  Hand-book  of  Minerals 16mo,  mor.  3  00 

Chester's  Catalogue  of  Minerals 8vo,  paper,     1  00 

Cloth,  1  25 

*  Crane's  Gold  and  Silver 8vo,  5  00 

Dana's  First  Appendix  to  Dana's  New  "System  of  Mineralogy".  .Large  8vo,  1  00 
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Large  8vo, 

Manual  of  Mineralogy  and  Petrography 12mo,  2  00 

Minerals  and  How  to  Study  Them 12mo,  1  50 

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Text-book  of  Mineralogy 8vo,  4  00 

Douglas's  Untechnical  Addresses  on  Technical  Subjects 12mo,  1  00 

Eakle's  Mineral  Tables 8vo,  1  25 

Eckel's  Stone  and  Clay  Products  Used  in  Engineering.      (In  Preparation). 

Goesel's  Minerals  and  Metals :  A  Reference  Book 16mo,  mor.  3  00 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) 12mo,  1  25 

*  Hayes's  Handbook  for  Field  Geologists 16mo,  mor.  1  50 

Iddings's  Igneous  Rocks 8vo,  5  00 

Rock  Minerals 8vo,  5  00 

Johannsen's  Determination  of  Rock-forming  Minerals  in  Thin  Sections.  8vo. 

With  Thumb  Index  5  00 

*  Martin's  Laboratory    Guide    to    Qualitative    Analysis    with    the    Blow- 

pipe  12mo,  60 

Merrill's  Non-metallic  Minerals.  Their  Occurrence  and  Uses 8vo,  4  00 

Stones  for  Building  and  Decoration 8vo,  5  00 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

8vo,  paper.  50 
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Domestic  Production 8vo.  1  00 

*  Pirsson's  Rocks  and  Rock  Minerals 12mo,  2  50 

*  Richards's  Synopsis  of  Mineral  Characters 12mo,  mor.  1  25 

*  Ries's  Clays:  Their  Occurrence.  Properties  and  Uses 8vo,  5  00 

*  Ries  and  Leighton's  History  of  the  Clay-working  Industry  of  the  United 

States 8vo,  2  50 

*  Tillman's  T^xt-book  of  Important  Minerals  and  Rocks 8vo,  2  09 

Washington's  Manual  of  the  Chemical  Analysis  of  Rocks 8vo,  2  00 


MINING. 

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Boyd's  Map  of  Southwest  Virginia Pocket-book  form,  2  00 

*  Crane's  Gold  and  Silver 8vo.  5  00 

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*  8vo.  mor.  5  00 

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Eissler's  Modern  High  Explosives 8vo.  4  00 

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Ihlseng's  Manual  of  Mining 8vo,  5  00 

*  Iles's  Lead  Smelting 12mo.  2  50 

Peele's.  Compressed  Air  Plant  for  Mines 8vo.  3  00 

Riemer's  Shaft  Sinking  Under  Difficult  Conditions.     (Corning  and  Peele).8vo.  3  00 

*  Weaver's  Military  Explosives 8vo,  3  00 

Wilson's  Hydraulic  and  Placer  Mining.     2d  edition   rewritten 12mo,  2  50 

Treatise  on  Practical  and  Theoretical  Mine  Ventilation 12mo.  1  25 

17 


SANITARY    SCIENCE. 

Association  of  State  and  National  Food  and  Dairy -Departments,  Hartford 

Meeting,  1906 8vo,  $3  00 

Jamestown  Meeting,  1907 8vo,  3  00 

*  Bashore's  Outlines  of  Practical  Sanitation 12mo,  1  25 

Sanitation  of  a  Country  House 12mo,  1  00 

Sanitation  of  Recreation  Camps  and  Parks 12mo,  1  00 

Folwell's  Sewerage.      (Designing,  Construction,  and  Maintenance.) 8vo,  3  00 

Water-supply  Engineering 8vo,  4  00 

Fowler's  Sewage  Works  Analyses 12mo,  2  00 

Fuertes's  Water-filtration  Works 12mo,  2  50 

Water  and  Public  Health 12mo,  1  50 

Gerhard's  Guide  to  Sanitary  Inspections 12mo,  1  50 

*  Modern  Baths  and  Bath  Houses 8vo,  3  00 

Sanitation  of  Public  Buildings 1 2mo,  1  50 

Hazen's  Clean  Water  and  How  to  Get  It Large  12mo,  1  50 

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Control 8vo,  7  50 

Mason's  Examination  of  Water.      (Chemical  and  Bacteriological)..  .  .  .  12mo,  1  25 

Water-supply.      (Considered  principally  from  a  Sanitary  Standpoint). 

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*  Merriman's  Elements  of  Sanitary  Enigneering 8vo,  2  00 

Ogden's  Sewer  Construction 8vo,  3  00 

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Parsons's  Disposal  of  Municipal  Refuse 8vo,  2  00 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 


ence to  Sanitary  Water  Analysis 12mo, 

*  Price's  Handbook  on  Sanitation 12mo. 

Richards's  Cost  of  Cleanness 12mo, 

Cost  of  Food.     A  Study  in  Dietaries 12mo, 


50 
50 
00 
(JO 

Cost  of  Living  as  Modified  by  Sanitary  Science 12mo,      1  00 

Cost  of  Shelter 12mo.      1  00 

*  Richards  and  Williams's  Dietary  Computer 8vo,      1  50 

Richards  and  Woodman's  Air,  Water,  and  Food  from  a  Sanitary  Stand- 
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Rideal's  Disinfection  and  the  Preservation  of  Food 8vo,     4  00 

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Turneaure  and  Russell's  Public  Water-supplies 8vo,     5  00 

Venable's  Garbage  Crematories  in  America 8vo,     2  00 

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Ward  and  Whipple's  Freshwater  Biology.      (In  Press.) 

Whipple's  Microscopy  of  Drinking-water 8vo,     3  50 

*  Typhoid  Fever Large  12mo,     3  00 

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Winslow's  Systematic  Relationship  of  the  Coccaceae Large  12mo.     2  50 


MISCELLANEOUS. 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Excursion  of  the 

International  Congress  of  Geologists Large  8vo.  1  50 

Fen-el's  Popular  Treatise  on  the  Winds ...  .8vo,  4  00 

Fitzgerald's  Boston  Machinist 18mo.  1  00 

Gannett's  Statistical  Abstract  of  the  World 24mo,  75 

Haines's  American  Railway  Management 12mo,  2  50 

Hanausek's  The  Microscopy  of  Technical  Products.     (Winton) 8vo,  5  00 

18 


Jacobs's  Betterment    Briefs.     A    Collection    of    Published    Papers    on    Or- 
ganized Industrial  Efficiency «.8vo,  $3   50 

Metcalfe's  Cost  of  Manufactures,  and  the  Administration  of  Workshops.. 8vo,  5  00 

Putnam's  Nautical  Charts 8vo,  2  OO 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute  1824-1894. 

Large  12mo,  3  <H> 

Rotherham's  Emphasised  New  Testament Large  8vo,  2  00 

Rust's  Ex-Meridian  Altitude,  Azimuth  and  Star-finding  Tables 8vo,  5  00 

Standage's  Decoration  of  Wood,  Glass,  Metal,  etc 12mo,  2  00 

Thome's  Structural  and  Physiological  Botany.      (Bennett) 16mo,  2   25 

Westermaier's  Compendium  of  General  Botany.      (Schneider) 8vo,  2  00 

Winslow's  Elements  of  Applied  Microscopy 12mo,  1  50 


HEBREW    AND    CHALDEE    TEXT-BOOOKS. 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament  Scriptures. 

(Tregelles.) Small  4to,  half  mor,     5  00 

Green's  Elementary  Hebrew  Grammar 12mo,      1  25 


X 


on  seventh  day  overdue. 


1347 

LIBRARY  ilSE 

23  1052 


.087 
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